I don't see the problem. Lesnar was not KOed, he was just in a precarious position in which he continued to defend himself properly. Carwin foolishly punched himself out and failed to actually knock him out, then was too gassed to do anything and lost.
I'm not sure what rest period Brock got except in between rounds which happens in every professional fight on the planet. The ref never pulled Carwin off, he let him do whatever he wanted.
The ref also only stops fights solely when the attacked fighter appears to be very dazed and is not defending himself. Brock appears very cognizant the entire time.
If you break the fight down even more, Carwin only has an 8 second barrage, then Brock fight him off (kicks him off). Then Carwin has a second barrage of maybe 20 seconds after putting around a bit to get back into position. . .and is already clearly gassed even during the last 5-10 of seconds of that second barrage. Then he barely does anything for the rest of the fight.
The announcers even start talking about Carwin punching himself out very shortly after the second barrage when it was clear he had nothing left.
After all, Carwin's never gone to the 2nd round before until that fight. He just expects people to wilt under the pressure and Brock didn't. You also have to give the champ the benefit of the doubt and expect he'll come back unless he's KOed. . .which again, Brock wasn't.