I'm of the mindset that earned play time is as valuable if not more so than immediately being gifted 35+ minutes a night as a young player. That being said, I still think Fultz and Brown can see 20-25 minutes per night next season and develop just fine. Yeah, they won't have the counting stats of Westbrook/Durant/Harden etc did as young players, but they wouldn't need to with 3 vet all stars in the house. Overall, we could be looking at a team with 5-6 impact, all-star talent level players in the next couple of years. That is borderline unheard of.
Possible rotation with minutes to show development:
1 - Thomas (32), Fultz (16)
2/3 - Heyward (34), Smart (26), Brown (22), Crowder (10), Fultz (4)
4/5 - Horford (32), Zizic (20), Crowder (16), 28 minutes at the 4/5 spot still available for Yabs or another vet big pickup.
Rozier is obviously the odd man out here, so he could be kept at first while IT is coming back from surgery and then flipped at the deadline if necessary.
Brown and Fultz get 22 and 20 minutes in this rotation. Plenty of time to develop. If they outperform those minutes and demand more, then great. You've got another valuable trade chip in Crowder (or Smart I guess though he's my binky) that you can move for a big.