A build is more than just skills, its gear and skills together.
You can change 15 skill points around or 3 5/5 skills, and most your gear and have a build that acts completely different. I don’t care how a build looks on paper but how it plays.
With all the guns, shields, oz kits, com, and skill points you can make a lot of really different ways to play.
For example I could take my Deputy Jack, swap my Flayer for a Skullmasher, move a few skills and have a much different playing build for minimal change. But the build could be drastically different.
There are 1000’s of ways to play this game, not 20 ways is what I’m saying.
Maybe instead of looking at standard builds, go look at a gun you want to use and find a way to make the most out of it. Thats how I make my builds often, I grab a gun or a com and think to myself, how can I get the most out of this. I don’t look at others builds, I just look at what is in front of me.
How many Nishas spec 3rd degree?
How many Jacks spec PtR?
How many Clappys spec anything melee?
If the answer is not a lot, there’s no way build diversity has been exhausted. Would the Unkillable melee siren have existed if no one thought to experiment with 'recompense? How would Zero players have discovered the “dangerous method” if no one specced CA? What about Backdraft Maya, melee Sal, or any other of the niche builds in BL2? No one could have discovered these builds if no one ever specced those skills. As long as there are skills that a aren’t being explored, there’s no way build diversity has been exhausted.
Slight derail, I would suggest giving it a go. Its quite a different experience to see the jacks you sacrifice like their nothing wipe out a whole room of enemies without any help from you. Personally, I find it hilarious.
Short answer no, long answer is complicated I’ll get back later and elaborate.
Quick examples: everyone has a chronicler build as all chroniclers are good, very little exploration gone into Claptrap (not much farther we can go admittedly but you forgot to mention nova-tp, which also has two incarnations, Jakobs Trap, and DoT/Tank/Support trap which hasn’t been explored at all), Hybrid nisha hasn’t been explored much (her left tree is more than just stacks), Jack has basically infinite builds (I wish there were better COMs for dedicated pet builds), Wilhelm’s kinda boring, but there’s still exploration in dedicated tank builds.
There are also cool idea things like tediore Athena that are viable too but haven’t been explored much if at all, but we’ve hardly explored all viable builds…not even close