Ugh. Let me get this straight. You'd like to sign Smart for 4yrs @ $50M. Turn around and deal MaMo for a ham sandwich (due to salary/repeater purposes). Then deal Rozier (who didn't yield a first rounder last year) this Summer for what? Because you think Rozier's defense is Kyrie-like?
Yes.
I'd try to trade Rozier for a guy on a rookie deal that can be a cheap bench guy for multiple years when they'll likely be in the tax. A Josh Hart type(EDIT: looking a bit into this, maybe Celtics could get Wes Iwundu and OKCs top 20 protected pick from Orlando for Rozier. Or Davon Reed and Milwaukees protected pick from Phoenix.)
I don't think it takes much to see a minute crunch here, the regular season doesn't matter for this team so I'm looking at the playoffs. They can play the non-rotation guys they want to develop like Williams, Semi, and Wanamaker(to a lesser extent) to get them through the regular season if necessary.
Figure your top five guys play the 36 minutes a game that Horford/Tatum played this year. That leaves 60 total minutes for everyone else. I'd figure Baynes/Theis to play most, if not all, of the 24 minutes that Horford/Tatum are on the bench. I think Smart plays a minimum 20 minutes, I think it'll be more mid 20s, at the point/wing. Say Smart/Baynes/Theis combine for only 40 minutes. That leaves 20 minutes total for Morris/Rozier/Semi/anyone else they pickup or earns minutes.
Doesn't feel like nearly enough to me.
Then considering Morris and Rozier are going into a season where they're looking to earn their next contracts, and their trade value is likely as high as it will ever be for Boston, I'd look to cash them in.
If Smart is here on the QO, I'd probably keep Morris since he's decent depth for injury concerns, likely doesn't have much trade value, and the tax wouldn't be an issue. But I'd have zero issues moving him to avoid tax if necessary. He's a luxury item.