Of course he was calling Booker stupid. It was hilarious. That whole set with Jericho is one of Jericho's favorite career moments for a reason.
Booker lived to win Titles. Just like Kane survived being called a "big red retard", just like Big Show survived being called a 500lbs bag of monkey crap, just like Hunter survived being called a boring, big nosed brown-noser. The only talents that were "ethered" were under-talented performers who couldn't get their heat back, like Billy Gunn.
The biggest difference between a Rock promo and a Cena promo is Rock sells intensity. He never let's you forget that he wants to fight the guy. His work with Cena was hit or miss at best, but I saw more classic Rock in the Punk feud.
I think the other reason I was not a big fan of the Rock/Booker T feud is because the WWE were pretty much burying any talent they carried over from the acquisition. I remember joking at the time that had Sting gone over with the rest of the WCW guys, Vince would have jobbed him out to Crash Holly.
In any event, I wasn't a fan of the Rock/Booker T angle. Had Booker been a bit more established with the roster at the time, maybe it wouldn't have bothered me as much.