I definitely think the lack of experience on the bench will hurt. I don't care about age, I care about experience. Jaylen has one year. Rozier only about 1.5 years and that half year at just 8 mpg. Tatum, Theis, Ojeleye, Nader, Yabusele, Bird and Allen have no NBA experience. And I don't care about Theis' experience in Europe. Bench players in Europe don't usually, if ever, make it in the NBA. Usually only European stars and starters that are in older than 21 have NBA careers once they leave Europe.
If Horford misses 10 games(which he did last year) or Irving misses significant time(which he has in the past) this team is screwed. Heck, when the starters get in foul problems in games, its going to mean Stevens ryling on rookies.
Inexperienced teams don't win tons of games. Half this team has little to no NBA experience and over 1/3(not counting the 2 way contract players)are rookies.
For this reason, I think this team takes a step back.