Crayo said:I believe at the time they didn't know how long they had Brock for or if they were going to run into issues with his contract, so they rushed it (hence why their match was at Extreme Rules) and put Cena over.
I'm just going from memory (of dirtsheets too), but I don't recall any problems coming up with Brock's contract until he stated something along the lines of wanting to return to UFC after his stint in WWE was done (or something to that effect) and that didn't happen until after Brock had "broken" Triple H's arm. I don't think it was rushed at all.
I think they decided after building up how big of a match Rock/Cena was to Cena, including having Cena say something about how "this is the most important match in his career", and then deciding to have him lose, it was important to re-establish that he still Super Cena. So, they debuted Brock, had him booked as a dominant force ass-kicker, and have him lose to Cena at Extreme Rules so that they Cena would "bounce back" from his lose against The Rock and they wouldn't need to worry about dealing with the fact he lost the most important match in his career and just go on booking Cena as normal. So in less words, they used Brock to make sure Cena wasn't hurt from his loss to Rock. And I've already detailed in a previous post how much better having Cena losing to Brock would've been and I don't want to sound like a broken record so I'll stop here.
That said about their Extreme Rules bout; the finish was absolute atrocious and beyond idiotic; I still love the match because everything prior was incredible but it doesn't top my top three of the year anymore unless I'm in an extremely forgiving mood.