Rock wasn't holding back anything, heel or face he would've said pretty much the same thing with more insults added in.
Every wrestler delivers promos in their own way. I don't understand why some fans haven't figured that out yet. CM Punk cuts a shoot style promo, that's HIS style. You will NEVER see Cena or Rock or practically any other guy on the roster cut a promo like him because that's HIS shtick.
Rock delivers his promos with a good balance of intensity and comedy which is hard to master as Cena has tried for years to find this balance himself and fails as he's either too intense or too comedic.
Rock also manages to put over the guy he's facing to build them up in the fans eyes while at the same time tossing in a few insults so in the end they're at the same level to the viewers. Notice how Rock went back and forth of mentioning Punk's title reign and talent while making fun of his looks?
Some of you ignorant haters need to realize that these two will never cross into each other's shticks. Punk won't be making jokes and spitting out catchphrases and Rock will never "break the 4th wall" bringing up the non-kayfabe issues in the WWE.
That's not who Punk and Rock are and that's not what we know them as. We know them as two talented men both on the mic and in the ring with two different styles on the opposite ends of the spectrum who just so happen to mesh so well when put together in the ring better than Cena could ever hope to be.
We have two more episodes of Raw for their promos to build up into something amazing, this was just a taste of what's in store.
So stop spitting it out, fucking swallow it and enjoy.