Cena beating Brock was fukking stupid, but Brock wasn't gonna stay to be a regular anyway. And you know damn well they would have fukked the booking if Lesnar won and they tried to build a rematch for Summerslam.
The three big things out of that RAW were:
Brock (part time guy, can't build around him)
Rock saying he's gonna be WWE Champion (part time guy, only coming back on 2013, can't build around him)
People being pissed as fukk about D-Bry losing and starting the "YES!" boom. And for the most part, the E has capitalized on that.
So, in hindsight, there wasn't much there to keep the momentum from Mania and the RAW after.