Title kinda says it all. There are a few builds and quite a few more Legendary weapons that, despite having a definite ‘cool’ factor, simply don’t hold up when thrown at Mayhem 3, or sometimes even Mayhem 2. Lemme know if you’ve found anything else that also doesn’t quite live up to the standards many, many other guns, builds, and gear items bring. 
For starters, we’ll begin with Fl4k’s entire Master tree. Why? Because it’s the one dedicated to making the most out of your pets and it’s… underwhelming. Really, really badly underwhelming. I don’t want my pets to kill everything for me, since this is a shooter and gun-focused game, but it’s pretty annoying that my Eridian Skag, while using Gamma Burst (And with a 65% Radiation Damage Anointed weapon) gets ruined by a stray psycho, and is utterly useless against anything carrying a heavy weapon. A lot of the tree’s skills do make a slight difference in how Fl4k’s pets deal with taking and dishing out damage, but as a whole it’s very lackluster. I feel that substantial buffs to pet survivability would do well, or, adding a new skill/modifying an existing skill that lets your pet gain a copy of your shield.
The damage from pets isn’t… great, but, it’s passable enough. As stated, making them too strong would kinda throw everything off balance-wise, so I don’t really have any bad opinions here.
Lastly… the final capstone, Dominance. It’s little more than a neat gimmick, which is a damned shame. The duration is awful, and sometimes I end up forgetting I have it equipped and now I have an enemy that I can’t do anything with because it won’t take damage until Dominance wears off. I’d honestly argue for maaaaybe a 25-50% buff to the skill’s duration, and then changing the damage-over-time the skill inflicts to a percentage of the target’s health, armor, or shields. The only time the skill is marginally awesome is for converting Badass heavy units, but then for that 12 seconds it takes pretty much no damage from the DoT and ruins an otherwise neat balancing gimmick.
Finally, moving onto Legendaries that don’t feel… well, legendary.
I’m gonna start this off with the Atlas Carrier. It’s a legendary assault rifle that, when the bullets hit an enemy, they split into two more bullets that seek out and hit more targets. It sounds awesome on paper… but the built-in damage penalty the gun has is far too extreme. 50% less damage just for being a Carrier absolutely cripples the weapon, and on Mayhem 3 you’ll expend 2-3 magazines into a single Shotgun Tink just to kill it. It’s a really cool weapon idea, but it lacks any form of damage to be able to use properly as a cool, unique legendary.
Hell, I’d argue pretty much ALL Atlas weapons need some numbers tweaking, because I’ve yet to find one that even feels half as good as a similar Dahl, Tediore (not counting reloads) or CoV weapon. The tracking bullets is a neat gimmick, but Atlas guns as a whole seem to suffer from horrendous actual, in-game damage output, especially when you consider they’re difficult to score critical hits with. Even when used from Fl4k’s ‘Fade Away’ Action Skill, they’re… meh, at best. You’d do better with pretty much any other weapon in it’s class than an Atlas, and that sucks. They look cool, let 'em be cool too, Gearbox.
A similar weapon in this vein is the Jakobs Monocle, a legendary sniper rifle that’s entire gimmick is an ABSURD scope zoom. Like… 18.6x scope zoom. Why? It’s almost always inferior damage-wise to any Jakobs purple sniper rifles, and the rest of it’s stats aren’t much better. If you’re going to do a ‘cool scope’ legendary, why not go for something aside from high zoom, a feature that is just about wholly useless in I’d say 90% of Borderlands 3’s maps and arenas. Why not let it highlight weak points, or, gain damage the longer you scope in?
Anyways, that wraps up my current gripes with builds and legendaries that don’t feel like they’re at the full potential of where they need to be. And, no, I’m not basing this on some builds being ‘overpowered’ in comparison… In every Borderlands game, there’s always one or two builds per character that absolutely shine compared to others, but in BL2 it seems there are also some builds, weapons, and skill trees that just… well, suck. And I think some easy tweaks (Except for the Monocle… that one’s tricky) could make everything ‘feel’ a bit more normal, while still letting OP builds be OP.
