Wait. So you think the reason why he is underpaid is that he says obvious stuff? Trying to understand your point.
He is a top 5 contender and is def favorite if he faces the current champion. His fights are exciting to watch. So what else the UFC needs to pay this man what he deserves?
No, the reason he is "underpaid" (we'll get to whether he really is in a moment) is that he apparently doesn't understand the first thing about promotion - and comments like the Rousey ones prove it.
Plus it's not saying much that he'd be a favourite against the current champion. Pretty much everyone is a favourite against Bisping, that's part of what makes him being champ so funny.
As for paying him what he deserves, honestly, I think he's probably getting it. His disclosed salary at UFC2000, where he beat Thiago Santos, was $110k (looks like $75k base, $35k win bonus).
Everyone on the main card that night except for Amanda Nunes (who got $100k flat to WIN the belt in the main event - ouch) got paid more than him, but that'll happen when a main card is as stacked as that one. The only person on the undercard that made more than him was Jim Miller ($118k inc win bonus) and he's been with the promotion forever. Mousasi made more than Sage Northcutt, a
lot more than TJ Dillashaw (only $50k including his win bonus), Kelvin Gastelum and Joe Lauzon. And everyone that lost, obviously. It looks like Diego Sanchez and maybe Johny Hendricks would have out-earned him if they'd won... but they didn't.
So he's on a bit over $100k in fights he wins, and it looks like his contract is skewed to more like a 70-30 show/win split as opposed to the usual 50-50. He's not particularly charismatic, not from an especially big or lucrative market, and his record since coming to the UFC in 2013 isn't really that impressive. He's got a signature win now over Chris Weidman (in weird circumstances) but he's got losses to Lyoto Machida, Jacare and Uriah Hall and his other wins have all been over middling or past-it talents.
I'm not saying the guy shouldn't get paid. I'm just saying based on the way the promotion currently values talent, he's probably about where he should expect to be.