Bear in mind that the vast majority of today's wwe fans started watching after Rock retired. Cena is the big star of their tenure of wrestling fandom. Yes, Cena would get booed and Rock cheered, but the heat would be evenly distributed. Anybody else who was in there for the Rock's big return would just be ignored by the crowd.
And Cena doesn't write his promos now. He wrote his raps way back when, and they were a hell of lot more creative than Dwayne's "popcorn fart"/"you hump cows" shit was.
On the rare occasion where Cena is allowed to be an intense badass, he has shown that he can do that better than the Rock as well.
I know i'm just an "eight year old Cena fan" as they would say on YouTube, but somebody's gotta play devil's advocate to all you cool Attitude Era fans.
And btw, I completely disagree w/Cena about the Rock.