imo the only season we were rebuilding in the tanking sense of the word was Stevens' first year 2013-14.
-avoided any short-mid term commitment, such as signing a goodish FA.
-we gave lots of playing time to young players
-kept experimenting with rotations throughout the season
-arguably lost a couple of games on purpose (or did not try very hard to win; pick your terminology) to improve our lottery chances.
-and ofc we played half a season with Jordan Crawford as our starting PG.
This was both a choice, but also a necessity: Rondo was still in theory our best player but injured, and it only made sense to at least try Bass and J.Green as starters to see what they can do.
In CBS's second season, and esp. after the IT trade, we clearly made a push to make it to the playoffs. If you ask me we are a lock for the playoffs for the foreseeable future.
I do not see this however, as being an obstacle to developing young players; first, because we are a young team, and our accumulation of draft picks suggests we will probably continue being young; and second, because some of the best teams at developing talent are also elite (SAS is the best example, but GSW has not done a bad job with Barnes or D. Green either)
tl;dr unless by rebuilding you mean tanking the two are not mutually exclusive.