Is Rondo a good player? Yes.
Is Rondo a great player? I don't think so. He is very good, but not "great".
Rondo is a very good player, who has become overrated because he has been on a good team with other very good players and been in the playoffs a lot and had several very outstanding series. Folks remember those spectacular games and think he is a "great" player.
Rondo is a very good player, who has become overrated because of the cult of the triple double. The triple double is a gimmick stat. By itself, using it to compare very good to great players against each other is worthless.
Rondo is not improving. He was a better player several years ago. Hard to believe, but true.
Rondo is a pain in the ass. He is hard to coach and at times disruptive to the flow of the team. If he was a great player (see, James, LeBron), then, really, you don't give a shit. If his production level is Rondo level, then, I think, it becomes a pretty big negative. On the Celtics you had the big three who are strong personalities who can corral Rondo and are less affected by his crap. On most other teams that won't be the case.
Rondo being a pain in the ass and hard to coach, having a big flaw in his game that has to be worked around, and being not as good as some folks seem to think (thus not unexpendable), has had Boston trying to trade Rondo for years now. They haven't been able to find a deal where they can get equal value to what he provides to the Celtics unique situation. Which is fine. But, if Rondo was all that, why do they keep trying?
Is he a Top 5 Point Guard? Maybe. But, that is the wrong question. The Blazers don't need a Top 5 PG. They need more talent.
If they could get Rondo (talent) as part of a Boston salary dump or for future picks, then sure, get him. Boston won't do that. They big value for Rondo, or they will just keep him as a core piece.
Portland overpaying (Aldridge, or the #6 and #11) doesn't do the team any good.