This FanHouse commenter is the latest:
I enjoy MMA, but lets face it, It is like a triathlete good at(running, swimming and biking) but not great at any. Could you think of someone coming into boxing (after being a pro wrestler) and becoming heavy weight champ. I'm Happy for Brock (scary dude) but him winning proves that MMA is an overrated toughman contest. Still enjoyable but not much skill required. Brock brings down the creditbility of the UFC and MMA in general. I'll still watch though just like I would watch a street fight.Before Lesnar made his UFC debut, I was sympathetic to that argument. But I'm not anymore.
For starters, the idea that because Lesnar was a WWE star he somehow lacks credibility as a real athlete doesn't hold up to much scrutiny. Lesnar was a great college wrestler. He's a legitimate athlete. The fact that he took some time off from being a legitimate athlete to go work in choreographed pro wrestling doesn't change that.
And while it's true that Lesnar couldn't be the heavyweight champ in boxing, the comparison to boxing doesn't really work because the skills necessary for wrestling aren't a component of boxing the way they are a component of MMA.
As for the comparison to triathlons, I actually like that comparison a lot, I just disagree with the commenter above. If Lance Armstrong had announced that he was retiring from the Tour de France to take up triathlons and had become the Ironman champ, would anyone think that brought down the credibility of triathlons? I don't think so.
The bottom line is that Lesnar is a great athlete who's worked hard at MMA and deserves the credit he's getting. I don't think he's the best heavyweight in MMA (that would be Fedor Emelianenko) or even in the UFC (I'd pick Antonio Rodrigo Nogueira to beat him), but he is a good fighter who has taken on legitimate opponents, and I don't think his possession of the title belt detracts from the UFC's credibility at all.