There are a lot of things here that just don't make much sense. I agree with your assessment of Rozier (I've always thought he would top out as a Leandro Barbosa-level guy off the bench, but never actually win a 6MOY award, but he looks to be a bit above that level at this point), but that's about where you lose me.
Even if you disagree with my assessment of his potential surely we can agree that he will need minutes and shots to mature.
I don't entirely agree with that (practice time is severely underrated), but that's beside the point: Why are we worried how much more he matures at this point? He's a free agent after next season, and we likely can't afford him anyway, so who cares? He's already good enough to help us win a chip. It's probably is his best interest to be traded to help his stock in free agency, but that doesn't mean it's in our best interest.
For example, look at Jaylen Brown, He was barely given minutes in his rookie year and did not mature much in his game. It was only through increasing minutes and ample opportunities to prove himself that he developed.
No way. Jaylen Brown improved a ton his rookie year, and beyond that, he made huge strides last summer despite playing 0 minutes of meaningful basketball in that time. He's made huge strides this season as well, but lets not act like he didn't improve before Hayward went down.
Terry Rozier was able to prove himself through the opportunities given to him by Kyrie's injuries. Terry Rozier has been a streaky shooter this year. I think he will continue to be a streaky shooter for the next couple of years as he matures. Next year, Kyrie is walking through those doors. Kyrie is a proven All-star and a top 15-20 player in this league. He will be our starting point guard. If your thinking so what Rozier can lead the bench in scoring and get his shots and development that way, your wrong. The difference between this year and next year is Gordon Hayward. Gordon Hayward is a proven All-star who needs his shots. Hayward will be playing thirty minutes next year. The Celtics offense this year had a problem with scoring when Kyrie went to the bench. I imagine that Stevens will stagnate Kyrie and Haywards minutes to try and make up for that. Also to give Hayward the number of shots he should be getting in a game. Then Jaylen Brown and Jayson Tatum will need their shots as well. They are amazing prospects who in my opinion will both be All-stars. They are higher in the pecking order. They will also help to score and probably be stagnated as well.
Our offense works by moving the ball and generating open looks. Nobody is going to be force-fed shots. Everyone will be giving up shots to make room for Hayward, not just Rozier. But this ties back to my point above: if we aren't keeping Rozier long term, why should Danny care how much he matures/develops next year?
In a recent Bill Simmons podcast, Simmons said to Zach Lowe that he expects Rozier to get like 12 minutes next year if everyone comes back healthy.
This is a major exaggeration on Bill's part. Even if you ignore any minute reductions for Hayward and Kyrie coming off their injuries, you're looking at a minutes split something like this (this is very rough):
Irving (32)/Rozier (16)
Brown (16)/Smart (24)/Rozier (8 )
Hayward (24)/Brown (16)/Tatum (8 )
Tatum (24)/Hayward (8 )/Horford (16)
Horford (14)/Baynes (20)/Theis (14)
Unless we add another guard, the 96 minutes a guard will be played by some combo of Irving, Brown, Smart, and Rozier. Irving isn't likely to play more than 32 (he led the team with 32.2 mpg this year), and Brown will play some minutes at SF as well as SG (figure he plays 32 mpg total, with a 50/50 split), so about 16 mpg there. That leaves 48 minutes for Rozier/Smart/end of bench guys. I think it'll be a pretty even split, but even the biggest Smart lover/Rozier hater will have a hard time thinking that Smart averages 36 mpg.
And that's not mentioning what happens if anyone on the team gets injured (which would shift minutes toward playing smaller, and free up more time for Rozier/Smart/Semi/Morris/Theis)
That is not nearly enough minutes to continue his development and increase his value. You could argue that his replacement could not produce as well as he could for 12 minutes but those minutes could go to the starters or be developing someone else. It is not worth keeping Rozier for 12 minutes for a 1-year contending run. one year because he becomes a RFA and it will be hard to resign him.
Not to keep beating the same drum, but why are we worried about how much he develops next year? There's pretty much no way his replacement does as well as him. Those minutes will not go to the starters, since they'll already be getting enough minutes (and Brad doesn't like playing guys big minutes). As for using them to develop someone else: who? Abdel Nader? Jabari Bird? A late first rounder from this year? We will have a team capable of competing for a championship next year, you don't weaken a team with that goal just to develop a late first rounder or second rounder.
If Roziers value is the highest it will with the Celtics right now and his impact will be minimal if he stays next year. The clear choice is to trade him.
If his impact were minimal next year, sure. But that won't be the case, especially with his ability to score off the bench.
2019 draft is not projected to be as good as this year's 2018 draft. I suggest using roizer to trade up into this draft. Simmions suggested the Memphis pick and Rozier for Orlando's number 6. I don't think we should do that trade but I do believe a trade must be made.
There's no way Orlando would go for that. Make it the Kings' pick and they might. If they throw in a veteran guard to give us 80% of what Rozier does (either from them, or in a three-way trade, possibly involving Morris), I'd probably bite (depending on who's still available at #6).
But trading Rozier for poor value just to avoid "losing him for nothing" (which is disingenuous, since the minutes he gives on a championship run will be extremely valuable) would be a bad decision if we want to try and win it all next year.
Edit: Dang smilies changing "8 )" (without the space) to