Can't you do the same for just about every team's back half of the roster?
Yes and no. Obviously no one goes 1-17 strong, but the C's have an inordinate amount of inexperienced players that have no business being a top tier team. I've made the argument several times the last few seasons, that one of the reasons for this is that Ainge doesn't really think this team is a contender and he is just trying to find players that could be contributors once Tatum and/or Brown hit their peak (with the hope that their peak is a franchise player type level).
I mean look at the Bucks. They have no rookies on the team at all (even the TW aren't rookies). They have 3 guys in their 2nd year and 3 guys in their 3rd year. They only have 1 4th year and 1 5th year guy. Of their top 12 minutes getters only DiVincenzo is younger than Giannis. The Lakers, Clippers, Rockets, Sixers, Jazz, Nuggets, etc. aren't all that much different either. Teams that believe they can win the title don't stock their roster with 1st and 2nd year players, especially when those guys are late 1st or 2nd round picks.