I kind of wonder at this point if Smart (or even Rozier) should be starting, with Morris in a 6th man role. Rozier is a guy who might benefit from the open looks he'd get playing with the starters.
If you go with Morris as your 6th man, which I agree with, then Baynes should be your starter.
Baynes matches up defensively with other Eastern Conf Centers: Embid, Drummond, Thompson, Whiteside, Kanter, Valanciunas, etc.
Horford matches up with the skilled big players like Giannis, Simmons, Love, Porzingas, Ibaka etc. This is a better use of Al Horford
It feels like Morris is the 4th or 5th scoring option with the starting 5, he can be the primary scoring option with the 2nd unit. Offensively with the starters, Baynes can set physical picks, PNR, hit the jumper at the FT line or add offensive rebounding.
I'd expect Morris to get more minutes than Baynes with this rotation.
In conclusion:
1. Morris would add a nice scoring punch to our bench and a
nasty physical presence with Rozier/Smart.
2. Baynes would be a solid defensive Center and any offense he would provide would be an added positive.
3. Al Horford wouldn't take the physical abuse of playing a vast majority of his minutes versus the opponents 5.