This is always a difficult chicken and egg thing because it's hard to assess, without seeing these guys in practice or knowing their habits as professionals, teammates, or people, how they might have progressed if they'd been given more of an opportunity to play significant minutes -- at least now and then -- as opposed to spending their formative years in the league riding the bench.
I tend to think that you can't really know what you have in a young player if you never put him in a "sink or swim" situation at least once in a while. It is true, though, that some guys come into the league and they're really too raw to do well with that type of opportunity.
I really don't see the point, however, of drafting guys who spent 2, 3, or even 4 years in college and then sticking their butts on the bench. Either they have some NBA level skills or they don't.
When the Celts were legitimately contending, I could understand the rationale of letting player development take a backseat. We were playing for home court back then. The main guys got older, and then depth became an issue, and still integrating younger players didn't seem like a priority, which was frustrating. To Doc's credit, he worked in some guys like Glen Davis, Avery Bradley, and Jared Sullinger.
Where the team is at now, it frustrates me to see draft picks spending their first year or two pretty much just riding the bench and killing scrubs in the D-League. It's nice that the team is competing for the playoffs this early in the rebuild, but we're not winning anything of significance this season, and a lot of the guys helping the team win right now aren't going to be here in a few years when the team hopefully has the main pieces in place to actually make some noise. I just don't know what we're doing collecting all of these draft assets if the guys we draft are gonna end up on the bench.