The idea is sound - trade an overvalued stock while it's overvalued - and it's an interesting thought experiment.
Even factoring that in, I have a hard time finding a trade involving Smart that works for the team. Smart brings a lot to the Celtics that would be difficult to replace. Jaylen could step into Marcus's spot, but he's a long way from being able to do what Smart does on defense, and I'm not sure he ever gets there. It's also an important plus for Marcus that he does not need a lot of shots to be fully engaged, which Jaylen may need. That Marcus is also (for the moment) efficient on a few shots a game and functions as a secondary playmaker is a cherry on that sundae. Does plugging Jaylen into the starting 5 really help him develop? Maybe; I don't know, given the limits on his usage. Does it help the team *this year*? Almost certainly not. And that is where I lose interest in trading Smart. I still believe this team has a shot to come out of the East this year, and once you get to the Finals you never know what can happen. (See, e.g., GSW in 2016, when Draymond gets himself suspended while his team was up 3-1...). I do not give that opportunity up lightly.
Jay King has a great thread on what Marcus brought at the end of the game last night. While Kyrie closed on one end of the court, Marcus closed on the other.
https://twitter.com/ByJayKing/status/1085951733384261633?s=20