I understand the argument that you shouldn't give up young pieces to win in the short term.
That said, I think once you realize that you have the core pieces in place to compete for the Finals -- which the Celtics definitely have now that Tatum and Brown are at an All-NBA / All-Star level - every single season is win-now.
We assume that the Celts have several more years with Tatum and Brown under contract and healthy. That's not an entirely safe assumption based on what we've seen happen in the league the last few years.
Every season that Tatum and Brown are healthy and playing at a high level is a limited opportunity to go deep in the playoffs. It's unfortunate that because of the circumstances this season, by the time the team truly realized how good Tatum and Brown are, it was too late to make a move to shore up the bench.
I hope that Danny acts with urgency this off-season. Bringing back basically the same team plus a few more rookies is probably going to have more or less the same result. Could easily be "less" rather than "more."
The Celts were in some respects lucky to make the ECF this year. If Simmons hadn't gotten hurt, or if the Celts had faced Milwaukee in round 2, I think they easily could be gotten bounced in an earlier round.