Rondo is pretty special on both ends, just not in an orthodox way. Just because New Jersey failed to build a decent team around Kidd (letting Kenyon Martin go, depending on the woeful frontcourt of Jason Collins, Uncle Cliff and Krstic) doesn't mean it couldn't have been done.
Rondo is not pretty decent on the offensive end. He is well below average, which is one of the main reasons the Celtics lost the first two games in this series.
The Nets were done. They had just lost to Detroit, which was better in just about all facets and that is when they let Kenyon go. It was apparent that team wasn't going anywhere, especially with Kidd already being 30.
Unless you have Magic Johnson or Isiah Thomas you don't win championships building around a PG and each of those teams had a team full of great players around them.
1. Rondo is an average to below average scorer (depending on how well he's shooting his free throws). But scoring isn't everything. Rondo's one of the very best transition offense weapons in the league and a fantastic floor general. This is offense too. Very similar to Kidd in his prime in this way.
2. The Nets shouldn't have been "done." They had just finished taking the eventual world champs to 7 games (the best showing any playoff team had against that Pistons team). Kidd wasn't slowing down in the near future(he went on to average a triple double for the playoffs at age 33!), Martin and Jefferson were in their mid 20s, Kittles was still productive (but overpaid). Their combination of fearsome defense and transition offense had earned them 2 finals appearance and a heavyweight playoff showing.
The main problem keeping from ever making it over the hump in their 3 contending years with the Kidd wasn't the lack of an offensive superstar (they got one in Vince Carter the next year and got worse), it was their terrible judgment/luck in staffing their center position. From Todd MacCulloch to severely broken-down versions of Mutombo and Alonzo Mourning (both of them barely played), resulting in long stretches of Jason Collins (perhaps the worst offensive center and one of the worst rebounding centers of his era).
It's a shame that Krstic came along after Martin left. A Martin-Krstic frontcourt would have allowed them to field a more potent offensive line-up and sustain their transition attack (the Krstic/Collins frontcourt greatly limited Kidd in transition).