Durant is a spectacular player, but there was never a Durant for JB trade, straight up, that was discussed (reportedly). If I'm remembering correctly, the rumors were that BRK wanted Brown + Smart + multiple picks; we allegedly threw out Brown + White + #1 as a talking point.
How would our season look right now if we had the same roster as we do now, minus White and with KD missing 21 games? That's saying nothing about the future.
My opinion remains the same: a trade for Durant only made sense if the team thought it was probable that JB would leave in free agency.
Even assuming Boston made literally 0 other moves (except Muscala), I'd be pretty happy right now with a roster of
Starters - Smart, Brogdon, Durant, Tatum, Rob
Bench - Pritchard, Hauser, Grant, Muscala, Al, Blake, Kornet
That team would be much better positioned to win the title this year, next year, and the year after. And that is without any other moves, which I'm guessing may have happened.
We'd probably be better if it was Smart instead of White given how they've both played this year.
Boston could get lucky and win the title this year as constructed, but with Durant they'd be the HEAVY HEAVY favorite to win. No other team would be close.