Anywho Leo’s guide is more of a basics to shotgunning so it covers a lot more than just DPS but I can offer my two cents on shotgun mainhand DPS.
Fire at will (Opening shot passive). This is kind of a mixed bag but ultimately I’ve ended up dumping this. The free shells require you to pay more attention to your shell count (thus more time staring at your UI less at the fight), the effect wears off it you take damage (so a hard pass for HR)
Point Blank Shot: A very solid damage boost but requires you to be in melee range. If your offhand is a melee this is a no brainer. If it is a fight where you will be running around a lot (MT) you may be better swapping thisfor something else.
Withering Salvo: If you’re using Full Salvo, get this.
Cleanup Crew(forget the name): Cleanup is too situational and finicky to be a reliable cleanse HINT DEVS so this is a waste of space.
Shell Expert: Passive that makes a good skill better. Yes it forces a reload on you but give how energy hungry your weapon is the extra energy is nice. The passive lets you keep the option of the shells you salvage with (can bite in you the butt if you are salvaging away greens) and gives you 5 offhand energy.
Fatal Funnel: CQC is already pretty situational for DPS, needing to impair a group is even more so.
Cluster Bombs: If you’re running Bombardment you should use this as well.
Odds and Evens: Mandatory for doing damage. Get this. Shotgun eats a lot of energy so weaving Power, Basic shots helps with your energy regen and this passive gives a reliable damage boost for it.
WP shells: This is a very solid passive outside of a few fights (HE2 the boss cleanses this each time he runs so you can’t really get much burn time going)
Enrich: I more or less skip this but if you’re one of those adjust your build every fight types might be useful in fights where you can’t benefit much from WP shells. Just bear in mind the default and advanced weapon UI do not show the bonus 2 shells, they come up as 2 stacks of a buff on your character. Need to test to see if they treat you as 6 shells for all of these shots or not.
Munition Expert: I disagree with Leo on this one and don’t run it myself as I run 5 shotgun actives so the odds of getting Green shelled is low but if you’re a ranged offhand as well could work in lieu of PBS.
Combat Reload: Hard pass. This passive creates more problems than it solves.
Bombardment vs Full Salvo: Salvo generally wins out due to overall usability, Bombardment is not as good on bosses that run move around or have STOP FIRING phases. Bombardment picks a target in the circle so it might grab an add instead of the boss for the main hit. Full salvo also applies shell affects (exception being green shells, it only procs their effect once a second) while ignoring the 1 proc a second rule meaning you can apply 5 stacks of DB, 5 DU damage procs or several AP procs if you’re lucky. Bombardment can apply exposed however if your teammates do not have ways to keep it up on the boss.