OK, fair argument regarding Rozier's ascension. But Rozier's minutes expansion in the playoffs was partly because we needed a point guard in Kyrie's absence. If Horford was the one hurt, we'd see Monroe get tons of additional playoff minutes over Semi but that wouldn't mean that he's gaining favor in the organization. Let's go back to your positional breakdown since I can see the merit in that. Sticking to saltlovers totals, that can be broken down as:
1: Kyrie (30) / Rozier (13) / Smart (5)
2: Jaylen (16) / Rozier (12) / Smart (17) / Hayward (3)
3: Hayward (17) / Jaylen (14) / Tatum (14) / Smart (3)
4: Tatum (16) / Hayward (10) / Morris (22)
5: Horford (30) / Theis (15) / Morris (3)
Granted, positional designations aren't that meaningful in Stevens' system, I don't think we'll see Hayward "at the 2" very much. Him playing at the SG would essentially require three of Kyrie/Rozier/Jaylen/Smart to be on the bench at the same time while three of Horford/Morris/Theis/Tatum are on the floor. It will happen, but not a ton, roughly as often as Kyrie/Rozier/Smart share the floor together.
Okay - so THIS is actually a useful contribution to the discussion. You are, as you say, using saltlover's original premises, Baynes is gone and we retain both Smart and Morris, and so Horford is forced to play all of his minutes at the 5.
This gets Smart to 25 mpg, while begging the question of: Why we would ever want him to play even just 3 minutes at the 3?
Seriously. On a team with Hayward, Tatum and Brown, (not to mention Morris, Semi and possibly Nader) what possible scenario ever calls for playing Smart at the 3 other than injury of extreme lineup weirdness?
Why wouldn't you play each of Hayward and the two Jays just one more minute each? Don't you want to win? I get that these are nominal numbers and we aren't talking about giving Smart 3 minutes at the three in every single game. But this notion translates to some ~240 minutes at the 3 over the course of the season. That just sounds like a terrible idea unless at least one of those guys ahead of him are injured for an extended period.
This is not the same roster that had Isaiah and Avery starting and weak wings and the need to throw 3-guard lineups onto the floor all the time. This roster is wing-heavy.
So even accepting the 3 saltlover premises, I see that walked back to 22 minutes for Smart right off the bat. It still begs the question of whether you believe Smart is deserving of 17 mpg at the two, giving him the _most_ minutes at that position when at least two of the other three you have dividing up the remaining 31 minutes are clearly superior players.
And this is all only really supported by the original premises, which force Horford to play all his minutes at the 5 -- after a season which showed how much MORE effective he is when allowed to play the 4 a lot!!!! This last year was arguably Horford's best overall season and a big reason was that he posted a Net-PER of +5.6 at PF (compared to a still very good +3.6 at C). Horford played ~43% of his minutes last year at PF and it was a raging success. Why do we want to walk it back?
If you instead acknowledge that we are better off playing at least SOME minutes with a true C (i.e, a Baynes/Theis type) up front and Horford at least SOME minutes at the 4, then that has a downward ripple effect. You aren't playing Hayward 10 minutes at the 4 and you aren't playing Morris 22 minutes there either. Not to mention that Semi guy will still be around.
In all his prior seasons, Hayward has barely ever played PF. His last full season at Utah he played almost exactly 50/50 at the 2 and the 3, with a tiny bit of time at the 1. And he was really, really good with this utilization, posting Net-PER ratings of +16.4 at SG and +10.2 at SF! Again, why do we want to deviate from that?
So more likely, it seems to me is that Hayward is going to get almost all of his minutes at the 3 and the 2. If Hayward splits his time across these two evenly, then we are talking about 15 & 15.
Now, if Tatum is also taking a fair chunk of time at the 3, then Jaylen is likely to get most of HIS minutes at the 2. I can easily see Jaylen getting 17-20 mpg at the 2 if not more. He's just too versatile defensively and can be played against pretty much every 2-guard in the league, big or small. Add it up, and very quickly Jaylen and Gordon have consumed 32-35 and maybe even more minutes at the 2-guard spot. That leaves just 13-16 minutes AT MOST to split between Rozier and Smart at the 2-guard spot.
Similarly, assuming Kyrie is able to come back and play ~30 mpg at the 1, there is only 18 minutes at that spot to split between Rozier and Smart.
So across the two guard spots, we are looking at a total of at most ~34 minutes for both Rozier and Smart.
Is the intention that Rozier will be marginalized back to a ~10 minute player? Maybe. But I doubt it.
But if you don't, how does Smart warrant the minutes to justify a $12-14M contract?