You’ve got the right idea; cover all the elements, but you can and should get rid of ones that are redundant. For any given weapon type I don’t see why one would ever have more than three guns (four if you use one for slagging). Either fire/corrosive/shock, or you’ve got a non-elemental gun that’s better than at least one of those three (possibly all of them, in which case you just carry that one gun instead). Also for specialty roles you don’t need a lot of spares - I never carry more than one slag gun, and very rarely more than one shock gun.
Only carry gear that you plausibly expect to use. Something like the following is what I typically do on all my characters: mid-range guns - fire, corrosive, shock, sometimes slag; close range guns - usually explosive or non-elemental (Harold, Torgue shotgun, Jakobs shotgun, or a rocket launcher); a sniper or two if I think the character can get some use out of it, but since snipers take a fair bit of work to one-shot enemies in UVHM I don’t usually carry much in this category. So that’s a total of about 8ish guns to carry, four of which are equipped at any given time. Maybe add a few more if you’re worried about running low on a particular ammo type (swap to a fire pistol or AR if your fire SMG is running dry, maybe) and I’m at 10-12, not a big hit to the backpack space. Same idea with grenades and shields, usually four of the former and 2-3 of the latter (adaptive, absorb, Bee). So typically my backpack is at 12-15 out of 39, plenty of room for loot!
I guess our tastes diverge on the Emperor, I love that gun. You have to aim down the sights to be effective with it (as with all Dahl guns), but it’s impressively accurate so you can lay full bursts on the crit spot from quite decent range. I’d rather have a Bitch (congrats on that one!) but the only one I’ve ever found was a Fatale (basically a cryo Bitch) in TPS…
Re: good ARs - I really like the Hammer Buster. Legendary Jakobs AR, do the Bane side-quest, then farm McNally in the Dust. I haven’t used it on Axton so it might not be as awesome with him as with Maya, but it should still be pretty good if you like Jakobs ARs. The Veruc has a good reputation as an anti-loader gun, and that’s also part of a Dust farm run. And although the Lyuda is a sniper rifle, functionally it can feel more like a very heavy AR with its large magazine and fast rate of fire. Drawing from the small sniper ammo pool is a negative there. Also a Dust farm (Veruc and Lyuda can drop from Mobley and Gettle after completing the Good the Bad and the Mordecai side quest).
I’ve had that same problem with rocket launchers. Probably that SBA Varkid wasn’t slagged, but still, you’d think the RL would do better. I’ll still use one in FFYL, but it may or may not get me up.