Remember that normally very durable Pierce was playing while injured this past spring.
I honestly think a Pierce / Green 1-2 punch at SF is more firepower at that position than any team outside of Miami or OKC.
KG is still KG. A top 5 PF or Center -> especially when only playing every other day in the playoffs.
Rondo can take over games, and does so with high frequency in the playoffs. He is surrounded by players that can hit the J at a high level (Pierce, KG, Terry, Lee, Bass), or at least at an average level (Bradley, Green, Sullinger).
The bench has the highest scoring ability of the KG as a Celtic era.
This team isn't the favorite, but they are a top 4 or 5 contender, with a very legit shot at the title.