When I played basketball in elementary and junior high, I was able to get away with being more athletic than everyone else. I was quicker than them and I hustled, so I could get ridiculous numbers of steals just by thieving from the unwary. I could get to the rim at will, so either scoring or setting up my teammates was a breeze even though I couldn't shoot very well. Then, I got to high school and suddenly there was more strategy and more athletes and more height and the tricks that I used to use didn't work as well anymore.
I say that because, to me, that's what I see in Rondo. Even at the NBA level he's going to be quicker and more explosive than almost everyone. So against most of the teams in the NBA on most nights he has the potential to kill them with speed. He can disrupt on defense, and he can break down their defenses by just being quick and decisive.
Unfortunately, like I found out in high school, there is always a higher level. And when we go against the ultra elite of the league, especially in crucial games, Rondo can no longer just out-athlete everyone. When we faced the Lakers in 2010, with their size up front and Kobe playing Rondo to shoot, his effectiveness went WAY down. When playing against the Heat, who have ultra athletes that are almost as quick as Rondo but jump a LOT higher we've seen Rondo be unable to finish effectively and thus lose a lot of effectiveness. And this is a problem, because teams like the 2010 Lakers or the current Heat are EXACTLY who we have to go through to get to the promised land.
Rondo is an excellent player. But the reason that he's not top-5 is that when other teams game-plan against him, his impact goes so far down. The Celtics as constructed can't depend on Rondo to be a top-5 player because he can't BE a top-5 player against every team. But the hope...what would have gotten them a title in 2010 had KG's knee been healthier, and what maybe would have gotten them past the Heat last year had Rondo (and maybe Shaq) been healthier, is that the team can do so many things in so many different ways. If everyone is healthy, then taking away Rondo's drives should open things up for the rest of the players on the squad to perform.
But to answer the OP, no, Rondo's not a top-5 player. But if everything else goes right health-wise on this team, we don't need him to be.