It's DEFINITELY not bigger than Rock/Lesnar II...all of those Cena matches never make money anyway. He's not a PPV draw so that doesn't matter. Lesnar vs Taker is not gonna sell out that arena next year...I guarantee it.
It makes way more sense than Rock/Lesnar II booking wise.
Taker/Brock - Picture this: Brock has beaten all of the top faces in WWE. Cena (we'll assume he get's his win back), Orton, HHH, Punk. He's beaten them all. For him, only one thing stands in the way of him proving to all that the WWE is just a big a joke as he said it was: the streak. The only man left for him to destroy is the man who one night a year is near invincible. Can he do it? Can he destroy the last sacred thing left in the WWE? Or will he end the streak and, potentially, WWE itself?
That's an easy match to sell.
Rock/Brock II - Picture this: Brock has beaten all of the top faces in WWE. Cena (we'll assume he get's his win back), Orton, HHH, Punk. He's beaten them all. All of them except for the Rock, who has returned from Hollywood to........make gay jokes about Brock.
Seriously though, Brock's WM match needs to be invincilbe monster vs. invincible monster, and Taker/Brock will do that better than just about any WM match in history. Rock, for all that he is (and he is a lot of things, one of which is being one of the most charismatic guys in history), he's never been this unstoppable fucking asskicking force of nature. As for Rock/Brock, how do you hype that match? You can't do all the wacky back and forth ala Rock/Cena. If Brock's talking about people shit their pants and that he doesn't give a fuck about WWE because he's a former UFC champ and he can whip anyone's ass, what does Rock do in that angle? Throw a Rock Concert and sing songs about Brock being ugly? That doesn't mesh well, imo.