I think Statements like "Brock will never be champion" are a bit on the extreme side.
1) Brock has only 7 MMA fights
and has all the resources in the world to train with the best people in the world. I think its not a matter of if he improves but how much he improves.
2) Matchup makes fights.
Say what you will about his standup but he is definitely a elite fighter when it comes to the ground game.
Cain beat Lesnar because lesnar couldn't take him down and keep him down. But who is to say that if say JDS beats cain, that JDS can do the same. Remember MMA math doesn't work. Just because Lesnar can't beat cain doesn't mean Lesnar can't beat someone that can beat Cain. (I'm not assuming jds will beat cain but that is just an example)
3. In the HW division, anyone can knock anyone out if they connect
We saw it before with lesnar hitting Randy on the side of the head. Although I would never favor lesnar over a guy like cain, if they fought 100 times, there is def no way cain would win 100 times. (maybe 99 times
all that said, odds are def against brock to regain his belt, but I would never count him out.