1. Kyrie-Rozier-Smart trios are not as unlikely as you think. In the 49 games last season which the three of them were all active, those three shared the court for a total of 178.5 minutes which averages about 3.6 minutes per game. The lineup was used in 43 different games out of the 49. Those lineups were a +9.5 differential in points per 100 possessions (+58 total on the season). So I don’t think they are that crazy nor that bad of a basketball idea and Brad seems to like them a little bit.
What this tells me is that Brad learned (or had the roster changes) to NOT use these 3-guard lineups so much. The prior season, he used Isaiah + Avery + Marcus together a massive 418 minutes (plus another 165 in the playoffs). He also used other 3-guard combinations including Terry. Overall, he had probably close to a 800 minutes using various 3-guard combos. Some of those lineup combinations were net positives (the ones with IT generally) but almost all of them were terrible defensively.
Now, a lot of that was driven by roster makeup. We simply didn't have that much wing depth and from Brad's perspective IT, AB & MS were three of his best players. So he contrived to keep them on the floor as much as possible. This meant using Marcus as a 'big wing'.
This last year's (and next year's) rosters are fundamentally different. We have massively better and deeper wing depth. This meant Brad had far less incentive to go with 3-guard lineups and only used them when they gave a clear and obvious advantage. Thus the net ratings for those lineups was good, as you point out. But really for only a tiny slice of minutes compared to the prior season.
I personally don't think we should really setup our rotation assuming we need to do that (use 3-guard lineups), given the return of Hayward (plus the increased experience development of Jaylen, Jayson, Semi & Nader) means our wing depth will be even stronger.
2. For a minute, I liked your idea of putting your best 5 guys in at their positions first. But the problem with that method is could end up pigeon-holing yourself to possibly need to play your 11th best guy more minutes than your 7th best guy. Don't you want to play your better players more minutes?
Well, it depends. Is my 7th best player really more valuable playing (and taking minutes at) the 1-2-3 positions as my 11th best player is at the 5?
Baynes may or may not be a 'better player' than Smart or Morris. But he's [dang] certain a better
center than either Smart or Morris. And we have lots of other players who are better at the positions Smart and Morris play.
3. We can't keep both of Morris and Baynes, it can only be one.
Well, I think this statement is only true if you assume we have to keep Smart.