I'm not sold on this idea "Rondo can't carry a team". For me, this means being the best player, not necessarily it's lead scorer.
In the beginning of the Big 3 era, Rondo was asked to be a complimentary player to the Big 3. This worked beautifully due to the strenthgs of the Big 3, and the complimentary skill set Rondo brought to the table. Now that the Big 3 are being asked to be the complimentary players to Rondo, it's not working as well. This isn't an indictment on Rondo though. The skill sets of the Big 3, at this point in their careers, just don't mesh well with the style of play Rondo is best suited for. They are slow and unwilling to attack the basket. They don't posses the abilities anymore to maximize Rondo's abilities.
Maybe, in a few years when Rondo has players surroundng him who can run, attack the basket, and score from the post, we'll truly be able to judge Rondo as a "lead dog". Until then, for me anyways, the jury is still out.