I actually think Tank is severely underrated, mostly because he should hang retired long ago, before his training regimen, or lack thereof, caught up with him.
But when you look at the first half of his career, he did accomplish quite a bit in his day...
He smashed Paul Varelans, a UFC tournament finalist, in about 12 minutes less than the legendary Marco Ruas did.
He went nearly 18 minutes with Oleg and gave us the first great fight in UFC. As far as cardio goes, he was actually in better condition than Oleg after the fight.
He destroyed Steve Jennum, who you'll recall was a UFC tournament champion.
He went the distance with Dan Severn, when Dan was the dominant fighter in UFC behind Royce Gracie.
Knocked out Cabbage quicker than either Sylvia or Arlovski. That's saying something.
His striking and wrestling were fairly solid for his day. His crude GnP was pretty effective, as well.
Then, sure, guys came along who were better, and like a lot of guys, he fell behind.
Tank never had the conditioning or the work ethic to match his strength and punching power, but he wasn't the talentless hack he gets made out to be.
Great post and the truth is we will not know who was better in their prime, mainly because Kimbo hasn't had his prime yet. Kimbo, while not young, is just getting into MMA and fighting 2nd tier guys. Tank fought the best back when the best was far better than the 2nd tier.
This discussion is really about 5-10 years from being positively determined. Let's just sit back and see if Kimbo actually keeps beating guys, because as of now I haven't seen anyone take his punches in an MMA ring and keep going. That's a bit shocking after watching Gannon eat his punches for what seemed like an eternity.