This isn’t criticism. The devs have a tough job. They can’t please all of the people some of the time and can’t please some of the people any of the time – damned if you do, damned if you don’t. It’s just something I think the devs should really give some thought to, i.e. the difficulty levels of Dark Agartha vs. cost effectiveness (risk/reward).
I have 2 toons – one a dps build (pistol/hammer – which I’d do differently, I think, knowing what I now) with 549 IP, and the other a healer build (rifle/fist), 522 IP. Decent enough that I can do the “seek and preserve” scenario at level 4 and sometimes get through the 3rd wave in the Occult scenario. (I can hear you veteran players thinking - Hell, I can do that with my bare hands lol).
Dark Agartha indicates that 175 IP for level 2 is best and 250 IP for level 3. (Might have the numbers wrong but close enough). Clearly, I don’t understand what those IP levels really mean. Because of my success with the other scenarios, I figured that my dps toon could probably do level 3, maybe level 4, certainly level 2. Nope. With potions, extra life, defense, etc., at level 3 my dps never made it to the Gate Keeper. At level 2, my dps did make it to the end a couple of times but was never able to defeat the Keeper. (At least, I can do level 1).
At level 3, my healer made it to the end once but promptly died. My healer can do level 2 consistently (with potions, etc.) even though he has a lower IP. (Which just shows how important healing is for Dark Agartha). But what’s the reward? Potions and a few fragments.
In order to get that glyph infuser (whatever it’s called), you need 300 fragments. Level 1 and 2 give 6 or 7 fragments? Less? That means, assuming I never fail, I need to do DA upwards of 50 times for one glyph thingy. Tedious but doable. Except that because I’ve had to buy potions, extra life, etc. I’ve spent thousands of Marks trying to do Dark Agartha. I have no idea what it would cost to get 300 fragments.
Now, if I weren’t successful in the other 2 scenarios, I’d say I was just a crappy player. (Hey! No comments lol). I have to think, though, the problem is with Dark Agartha. Its difficulty level is grossly skewed. It’s not in keeping with its supposed IP requirements; it’s not in keeping with the difficulty of the other scenarios; it’s not in keeping with the risk vs reward; it’s not in keeping with the time commitment or cost required to do Dark Agartha. True, I don’t have to do DA, and I don’t anymore. There is a loss in “fun factor” for the game over all, though. So, Devs, give a thought or two for adjusting the difficulty for Dark Agartha.
From my experience Dark Agartha has been more about how to approach the fights then the sheer difficulty of the fights. Having a cleanse, and impair and a decent self heal (most commonly cruel delight but at lower levels of crit a combination of passives and maybe thirst) are really important factors. Its hard for me to say at that IP level because I am further then that and don’t have any alts to compare but I know several people that had trouble and after suggesting a cleanse and impair and using them at the right time they had no issues. As for the rewards it may be a little underwhelming at lower IP levels but with the raised soft caps it is a nice little bonus later on.
The IP requirements are the bare minimum to enter that kind of content. You’re not expected to faceroll anything with the bare minimum. Quite the contrary.
Stonehenge and Dark Agartha, more than any solo content that came before, expect you to the able to adapt.
And in solo content you’re not a “tank”, “dps”, or “healer”, you’re a survivalist. Adapt.
I add also that, given your IP, you should be able to do higher S&P and OD than E4 and E2 (wave 3) respectively, so maybe you should reconsider your strategy.
On that note I cant help for DA other then general tips but for S&P and OD if you add me in game “Drenneth” im more then happy to run some of them as duo and give any tips if theirs something I think may help.
I don’t know if you’ve already tried this, but Anima Allocation also has a strong role in DA. Because the bosses hit hard, it can be a good idea to go for a 80/20 DPS/survivalist split. That way, you have more hp and higher protection so that you can take more hits.
As Drenneth said, it’s important to work out options for slotting in cleanses and impairs - gadgets are great, but the good ones are getting harder to come by on the AH because people are buying them for DA!
DA can be a pain to get used to, but honestly, the more you do it, the easier it gets. I know that’s frustrating when it’s costing you for every attempt, but as you get used to seeing mechanics and attacks, they become easier to avoid or counter.
In terms of rewards, you’ve got options. I agree, the fragment reward for the lower elite levels isn’t great if you’re saving for 300 of them. You do have the option though of selling fragments on the AH and using the MoF to help improve your gear. You can also choose to send all your frags to a single character and increase the number you’re saving (though the AP/SP cost isn’t great for that really imo).
DA is definitely harder at the thing it does than SP - ie. a single boss with a bunch of attacks. But to compensate it has no time limits on dps and you don’t need to handle aoes.
What you do need is solid self heals - in hammer that’s Pain Suppression. And impair/cleanses depending on the boss.
One paradoxical thing about SWL is that the “healing weapons” are not good at solo healing. At best they’re middle of the road and blood in particular is one of the worst cause of its self-damage gimmick.
I’d have to check but I don’t think smugly yelling “adapt” at people is useful advice, we’ll know for sure once I break out the graph paper. 
To the OP: the IP requirements for elite levels are the same across all content (and were lowered not long after launch to allow undergeared players to attempt higher level dungeons) so they’re not really an indicator of anything except which content you’re allowed into. Don’t use it as any kind of guide but also don’t feel like you’re failing by not attempting the highest tier you have access to - find a tier you can manage and then get better with practice.
As far as specific advice, do your characters only have those two weapons each unlocked? If you haven’t yet finished all of the actives and passives then the best advice I can give is (unfortunately) not to bother with Dark Agartha yet because you will definitely see a greater (and faster) improvement to your character by buying all of the passives and capstones than you will from making your glyphs elaborate.
If you have completed everything, then make sure you have a decent selection of gadgets available - you can probably cobble together a workable build from pistol/hammer (maybe less so for ar/fist) but you need to be making use of the gadget slot too. Mistresses Bashosen, Asibikaashi’s Hoop and the healing drone you get for completing a certain number of seek and preserve scenarios are all must haves in my opinion and there are plenty of others that will come in handy too.
Expect to have to change your build between fights depending on boss abilities - it can be helpful to buy the item that tells you about each boss before you start for your first few runs so you can do a bit of advance planning rather than standing around reading ability descriptions while the clock is ticking.
Again though, don’t feel bad about starting out at elite 1 and only moving up once it starts feeling easy - nobody (or at least nobody who’s opinion matters ) is going to judge you for taking things at your own pace.
Hi there, I might be able to help!
New player, fairly fresh lvl 50 here. Playing Rifle/Fist at 175ip, I did DA the first day, got to boss and died and failed. Have done it every day since then successfully, including the last two days on the 175 required level while my own IP was 225ish.
Build
LMB: Burst Fire
RMB: Feral Regrowth
Placed Shot
Incendiary Grenade
High Explosive Grenade
Vital Shot
Red Asibikaashi’s Hoop
Anima: 90dmg/10survival
Basic approach is just do the burst until grenade loads, placed until cooked then either HE if up or Incendiary.
Any time my life goes down to 75% I use feral regrowth. Any time that’s not enough healing, I immediately stop all dps and just spam vital shot until full health (except for maybe HE grenade).
The things that are really hard and nearly kill me are some bosses had stacking dots and thats what the gadget makes basically a cake walk.
You are supposed to have an interrupt for the last boss on his channels, so a gadget swap is probably appropriate here and I might need to do it for harder difficulties… but so far I can just regrowth/vital shot through his channel and then continue dps’ing once I stabilize.
Edit: I agree the rewards seem a bit underwhelming for 15 minutes of pretty tough combat. Additional distillates or maybe a dossier chance would be nice… or some DA only drops?
Just spitballing but I would prefer to drop feral regrowth to take an interrupt (which could then be from any weapon you have unlocked). He is significantly easier if you have Asibikaashi’s hoop cleansing his anti-heal effect.
HEG also interrupts if you can time it right but yeah, inconvenient compared to some.
I didn’t even know he had an anti heal effect. My only choice for weapon based interrupts are claw eviscerate (which requires melee range right and could glance, which basically means I die?)… I liked feral because it saved energy from rifle being spent on sustain and let me blow it on damage. Any ranged weapon interrupts?
Does glancing with an interrupt actually stop the interrupt effect from happening? I don’t think I’ve ever seen that happen - as far as I’m aware a glance just reduces the damage.
Yes, glancing will stop the interupt effect from happening.
Technically a lot of bosses do (it’s the 3rd item of debilitate/expose/corrupt which is a fairly common set - debilitate is do less damage, expose is take more damage, corrupt is heal for less) I believe his is a specially named one worth 5% per stack, don’t have a screenshot handy though. I start to really feel it around 5-6 stacks.
Any of the bosses can have the Weakening effect which will stack up debil, exposed and corrupted. It’s one of the times that having a cleansing drone gadget can be useful, as it’ll purge 1 effect per second when active. Only problem with the drone is when the boss also has the Purging effect, as that can get rid of your drone.
One of the things which I’ve noticed on alt runs is the difference that having a gadget cooldown reducing signet on your waist tali makes. You can cleanse yourself a lot more which really helps.
So I tested and this isn’t true, if you glance with an interrupt it still interrupts. 
And yet if you glance a Searing Brand interupt, you take it in the face. /shrug
I’m not going to discount the possibility that some dungeon bosses use entirely different rules to the rest of the game (because I’ve seen Darkness War) but I’ll try testing that next time I’m in Hell Raised.
I think it’s CC that doesn’t apply when you glance (knockdown, knockup, etc.) and if the interrupt is from the CC it doesn’t happen? Bosses have special rules though because they can’t be CC’d.
In that video I posted I knock a guy down with a glance.
Like I said, I’m not going to discount the possibility that it’s different rules for bosses but if it is I’ll be reporting it as a bug.
Edit: after 2 plus hours clowning around in e7 dungeons with no talismans equipped, using nothing but interrupts, I glanced a total of zero times, so maybe the way the “Immune to CC” buff is implemented means that interrupts can’t glance dungeon bosses? Who knows.