Trading Schroder, J-Rich, Smart, and Horford -- that all makes sense. These guys are not part of the future, in all likelihood. We do need to replace them with guys who are better at spacing the floor and moving the ball.
Even doing that, though, won't solve one of the major problems with the offense. To do that, you need to find somebody to be the primary playmaker who is a clear upgrade over Schroder and Smart.
I don't see a player like that out there who is realistically available for what the Celts have to offer (unless the Celts give up a core piece, which would be counter productive).
So yes, trade the vets. But it is probably going to require finding a talented guard in the draft who will hopefully be able to come along pretty quickly and become the dynamic playmaker this team desperately needs.