I don't think their attitudes/tantrums are equal at all. I question Cousins' attitude & work ethic a lot more than Rondo's. We have a pretty good read on Rondo & his track record. I still think the jury is out on Cousins. He's a much bigger question mark in my eyes.
I'm also not sure who has the higher ceiling. I lean towards Cousins but its awfully tough given one is a guard while the other, a big.
I'd say Rondo's ceiling is best PG in the league. He can pass Chris Paul with dedication on defense, a commitment to keeping the ball moving and improvement at the line (the last of which I honestly feel would open a whole new world for him anyway).
Cousins' ceiling, in my opinion, is that of the second-best center in the league. Dwight Howard, assuming he gets healthy (I think he's still only at about 75%), is going to be the best for some time. Cousins is already more skilled and is a better FT shooter than Howard will ever be, but he can't match the sheer physical dominance and huge defensive impact that a healthy Howard provides.
I don't really question Cousins' work ethic, but his attitude and maturity issues could keep him from ever becoming an All-Star (which, for his size and talent, should be a given). He needs to start respecting somebody or he'll be a bust.
I think KG and Doc could get through to him a lot more than the Sacramento environment can, so I'd be willing to take the chance. For Rondo? No. But for anything else, yes.