There are arrows you can use to nerf their armor. Weapons you can use with high armor penetration, and weapons you can combo that provide sunder for you and your thrall.
I usually carry a sunder weapon with me to help my thrall hit harder. That or put it on your thrall.
Actually if you take a look at this:
Mammoths are a step above Mastodons when it comes to both health and armor amount…
So @Taemien was 100% correct in saying that armor penetration is the thing you want… regardless of whether or not you’re wearing epic armor, it’s the weapon you use that’s going to be the determining factor here.
As an example look at what Blade of Seven Winds can do to a Mammoth…
With a war-axe that has 0 armor penetration I’d be there all day fighting it…
Sadly Sunder won’t do you much here, the issue with Conan and the Sunder debuff is that the armor jump is just too huge from creature to creature…
Sunder removes 10% of their ARMOR amount per stack… so 5 stacks = 50% armor value… however because of the amount of armor they have, cutting it in half is still going to be several thousand and the way the armor curve works, that’ll still net Mastodons 81% damage reduction…
That being said every little bit counts so sure… if your best penetration weapon that you can get there is a mace then having a few sunder stacks doesn’t hurt, just don’t die trying to refresh it as it’s worth just a few percent of armor pen 
I would point out that 81% damage reduction from 89% is actually significant. A 100 damage 0% armor pen attack goes from 11 damage to 19 damage. That is a ~73% increase in damage. TTK will be quite a bit quicker.
Combine good armor pen with sunder and you get some juicy results however. For example a Star Metal quality mace will have 50 damage and around 35% armor pen with a master weapon fitting (it’ll be even better with a decent thrall to craft it).
That 81% post sunder becomes 46% damage reduction after the armor pen. A 50 damage attack that normally would be 5 damage becomes 27 damage. Without sunder it would be 23. 4 damage increase doesn’t sound like much but it still results in around a 17% increase in damage, or in this case 20 less hits with the same weapon on average to kill the target (Siptah Mastodon).
Of course the Musashi’s Black Blade is pretty much the go to for such encounters. As shown in your video. There’s no need for sunders there. Even with nothing in Agility its still going to outdamage most strength based options against such highly armored opponents (we’re talking thousands of armor) 
You’re not supposed to be able to easily tackle everything in the game with beginner gear and/or a low level. That’s sorta the entire point of the game, progressively getting stronger.
Dots dots and moar dots!
for the record you only need 7 elephant hide to make each piece. So 35 for a full set.
I never let myself run out so when i get down to 40 left, i go out for more.
Use epic gear, legendary weapons and delving gear with bleed, sunder and /or poison.
Youll be walking away with much more plus the loot from storm creatures
In Siptah you have feroxic war axe and the one that I do not remember right now the name that applies sunder. So it’s very easy to go with 4 perks on agility, 3 in strength and smash each enemy before it knows what it hit it. But even full encumbrance and 3 perks on strength still works, just not so fast. Every weapon counts, it is always on the one who wields it. For example if I go with katana every stone of Siptah will cry from laughter 
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I don’t doubt that 
I was merely pointing out the ineffectiveness of Sunder.
Similar debuffs in other videogames pretty much remove armor proportionally and making enemies weak. In Conan it’s only really effective against targets that have player heavy-armor levels in the 1-2k range.
For example the Arena Champion / Judge has almost 19k armor… putting a full 5 stacks of sunder on her is the equivalent of a measly 2.47% armor pen… as such… relying on Sunder is just not viable in the case of heavily armored foes, although sure, if you can do it without any sacrifices then every bit counts like Taemien said
Also note that bleeds and poisons ignore armor, so you are 100% correct on the use of feroxic weapons in such cases
I was always going to my sweet mistress with my festering, not long ago an old teammate asked me a side challenge, to fix a religion weapon and armor to face a “good” boss. So I found the chosen one of Yog and I fixed the mace. You cannot imagine how fast she dropped down making me wonder why the hell I never came with mace to her with this weapon, if you charge attack, you’ll have all the combo to almost all the enemies. Later it needs either LLHH, or LLLH and the combo remains very effective, but charge and HHHH, is devastating to almost all the enemies, to some you don’t even complete the combo, they are already gone. The sunder is another bonus 
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I mean… you can. But you need to be good at being a murderhobo. 
The storm lands are not low level areas.
It is a known bug. Until the bug is fixed, those who do wish the difficulty spike should use the other 3/4 of the map until they are fully leveled and geared.
LOL! ill time it next time i go as im running ZERO in Agility or Strength.
And im already experimenting with various stats and builds.
The good news is my stockpiles of resources including rare ones are going through the roof.
I understand the point about other ways to get these things but is still seems self defeating from a game point of view because people will gravitate towards the easy way and no one will set up base on the hard side of the map. The devs talk about rebalancing this or that so how about rebalancing getting elephant hide to be the same effort where ever you are on the map.
This would mean placing elephants everywhere on the map.
There’s a particular design philosophy in creating asymmetric maps. It encourages exploration and expansion because you can’t get everything from one spot. If your spot has access to an abundant source of elephant hide, maybe you’re far away from the nearest deposits of gold, brimstone or black ice.
Sure, both maps have pockets where many resources are nearby. Maybe there could be a few more of them - but it’s unlikely that the maps will become fair for everyone once the first-comers occupy the prime real estate spots.
No, it would mean taking the storm creatures out of the area where the mastodon are. I get that there should be a reasonable amount of difficulty. Putting elephants everywhere would be too easy.