I have been playing since the game went into early access. In all honesty part of it is the game is getting a little old but another part of it is how different it feels compared to KF1. I played KF1 for the awesome shoot em up mechanics with really strong classes in general.
Now in KF2, everybody is a trash killer and big zeds are a bullet sponge. Not to mention that each of the classes feel weaker in their specialization if not just plain generic. The perk nerf bat no doubt has contributed to how burnt out I feel on the game. Almost anything good any perk gets is nerfed in some misguided sense of "balance" for a game that is largely supposed to be a co-op game, not a competitive game.
Support? Ammo cost nerfed, AA-12 nerfed
Commando - Ammo and recoil
Zerker - started out bad, became good, then got the nerf bat in damage for a strategy that exploits block(aka not swinging your weapon)
Medic - Armor healing nerfed for same strategy.
Firebug - Repeated click strat to save ammo and do more damage (but slower) nerfed. Now you just hold down the button and hope you have enough ammo.
Demo - Sucked on release, Nuke (the only reason you'd ever take the perk) was nerfed.
Gunslinger - new kid on the block, currently good but I'm betting that they'll nerf it.
I don't like nerfs in a co-op game. I don't play co-op games for competitive balance. The kill count matters little to me compared to finishing waves and the boss. (Hans melee is super strong right now).
As much as you can say "well KF2 is a different game" I can also say "it is the sequel to a game with specific mechanics I really enjoyed".
I played Zerker and Demo most in KF1. I liked that stunlocking scrakes with a katana was a reliable but not the fastest way to kill them (xbow), I liked that I had to play somewhat smartly with Demo not to blow myself up and not waste ammo. I had no problem with Sharpshooter one shotting scrakes and killing all things big zed related. Firebug - I liked that crisping the zeds was a unique mechanic. Only support and commando didn't interest me.
In general, it feels like players for some reason want to be the "best" in a co op game and developers seem to agree despite the gametype not really being the best for swinging the nerf bat. People care about content and if their perk gets stronger. Not if suddenly the thing they liked playing last patch is now a lot weaker because some people decided to take the nerf bat to the perk.