Dervish with Whirlwind Attack feat

[Ridley's Cohort]

WWA + DD is no more overpowered than power attacking and doing a leap attack while charging with a greatsword, which I'll bet sees way more use.

Agreed.

If it is such a target rich environment, the numerous foes are likely to be mooks. There is more than one way to skin a mook. Or a roomful of mooks.

If the targets are not mooks, you just dinged a lot of them without hurting any of them badly -- a tactically suboptimal choice in most situations.

WWA + DD may well be the freaking coolest way ever conceived of to smash mooks (I think so!) but I am not sure it is really more powerful than the alternatives considering the investment in a very long feat chain. An optimized brute with a Spiked Chain can easily just run in and crush 3-4 mooks without so much fuss.