I don't see the point in spending much time entertaining this fantasy, but I just want to point out that RPM in general, but DRPM especially, is not a static, end-all be-all stat that tells the defensive value of a player independent of context. The defensive stats are just too noisy to rely on them that much.
I'd have some concerns matching Horford and Okafor in the frontcourt, and Durant is, perhaps, not as impactful defensively as Crowder. The IT and Bradley pairing will always present some issues due to size.
Still, I think the fact that Crowder, Sullinger, and Amir are rated so highly in DRPM this year suggests the role that they play on this particular Celtics team. Crowder is a pretty good individual defender. Sullinger and Amir are just decent on an individual basis, at best.
I trust Stevens to make the most defensively of whatever piece's he's given, so long as there aren't absolutely glaring weaknesses.