A couple points:
Brock Lesnar will never return to WWE. Ever. As long as somebody named McMahon is calling the shots, I PROMISE that you will never see Brock Lesnar there again. The fans would not stand for it, neither would the guys in the back. His best shot is going to one of the B promotions, like TNA or back over to New Japan Pro Wrestling. But pro wrestling is not what he wants. It never was. Brock Lesnar is one of these guys that walked out of a Gold's Gym with a raw egg and an 8-pack and said "Hey! I saw a WWE truck go by, I'm gonna call them up, I'm a wrestler!" He consistantly botched matches, nearly ended careers, and in the end couldn't handle "the road schedule" and left with his tail between his legs. WWE invested millions and millions of dollars in Brock Lesnar, building character, merchandising, and storylines, just to have him back out.
In MMA, it's much the same. Brock goes to K-1 and destroys Min Soo Kim in 90 seconds with strikes. Video here --->
... This was a dominant performance, BUT, Lesnar outweighs Kim by a LOT, allowing him to power through his guard like a hot knife through butter. The level of competition in K-1 is nowhere NEAR Pride, much less UFC. And he steps in against Frank Mir, does okay for himself for a bit and then gets submitted in like 3 seconds. Lesnar has zero threshold for pain, if his strikes fail him, he doesn't know where to go. Unfortunately, for Brock, where he went was to the mat on the business end of a grapevined ankle lock from the guy who broke Tim Sylvia's forearm in two places. Video here --->
... Brock talked a lot of shit and had a lot of sizzle, prior to the one minute mark. Man's gotta spend a LOT more time in the gym learning the trade before he even thinks about getting this title shot that he seems to think he should get.
Brock's a punk. Always has been. And will continue to get his salad tossed in the UFC until he checks his ego and does the hard work.