As long as Stevens has most of his top 5 man rotations with 2 of Kanter, Tatum, Brown, Hayward and Walker, I personally don't have a problem with that starting lineup. What I don't want to see is basically two teams out there, the starters and the bench.
Last year
was a bit unusual in that respect, though lineups without starters were only found in blowouts.
But having said that, what evolved over the year was three men coming in as a sort of platoon at the 6-minute mark of the first and third, more or less: Hayward, Brown, and Baynes.
I thought I saw some really cool chemistry between Hayward and Brown - that's kind of what Hayward does, he brings everything together, with or without the ball. He's a lot more than a playmaker, let alone being more than a scorer.
In terms of the starting lineup, what really has changed?
Kemba replaces Kyrie. That should have a minimal effect on rotations.
Kanter replaces Horford. Al was already playing load-managed minutes (finished the year at 29), so while substitution patterns might be different, court time might not be.
Morris is gone. You could replace him in the starting lineup with someone of similar size who can guard the swings or even second bigs - that would be either Theis, Ojeleye, or Grant Williams.
Theis has played almost exclusively as the lone big (i.e., as the "Center") in his two years with the Celtics, so now playing him as the second big with Kanter seems unlikely.
Grant Williams is a rookie, and while it looks like he could earn meaningful minutes, it's also apparent that Semi is ahead of him.
The problem I see with starting Semi is that you do not have a second playmaker in the starting lineup - UNLESS you start one of Smart or Hayward.
If you start Brown/Hayward/Semi, that means that Tatum comes off the bench (unlikely). If you start Smart/Tatum/Semi, that means that both Brown and Hayward come off the bench. This is exactly what Brad did last year, with Morris as the swing, so it can't be ruled out.
What about two-big starting lineups? One possible future is that RW3 joins Kanter as starter; maybe we'll see some of that in February or so. But once Timelord has won the confidence of the coaching staff, it might be more ideal for Kanter to become 6th man, to give you scoring punch and put pressure on the offensive board. That way you can start Brown/Hayward/Tatum - a small lineup overall but with good rim protection.
Apropos, if Kanter is your lone big and Kemba your point guard, you rely on your three wings to do a lot of work to guard the 3-pt line and help protect the paint. In order to do that you could start Smart/Tatum/Semi, as I said earlier, or even Smart/Brown/Tatum.
He has to realize that after Smart, that bench is ridiculously inexperienced in the NBA with only Theis and Semi having more than a year familiarity in Stevens system.
Excellent point, though if everyone's healthy that's still an eight-man rotation, and beyond that they clearly want to get minutes early and often for the Timelord. And Brad Wanamaker is not only a vet, but played well enough to earn himself another contract (contrast with Shane Larkin).
(It's worth asking if Brad even has a "system", but I'm not going down that particular rabbit hole right now.)
In addition, two rookies are poised to get meaningful minutes this year: Carsen Edwards and Grant Williams. They look like they can play NBA defense in their rookie season.
Kanter is, but he is also clearly the best bigman on the team. I think his underlying point was, should the team start someone that is a worse talent than someone else for fit and other reasons.
In theory, the answer is of course yes. KGLL does not consider Kanter a role-player, apparently, while you do. I come down on the role-player side of that, with you - though I have misgivings about the whole concept.
Fit is more important, I suppose, than talent, though there's all degrees of both (which makes a hell of a difference). Maybe a better way to think about it is that talent is also part of fit, since fit is a function of effectiveness.
I'll end this before it gets any more conceptual.