Honestly, I don't think the culture in the locker room 'sucked'. I think the lack of accountability/professionalism in the front office was definitely a big problem, and to say that Doug Weight was in over his headis a massive understatement. But for all Jack Capuano's in-game shortcomings (and there were many), he was a functional, professional, coach who had enough of a reputation (and humility) to be proeprly employed ever since... unlike Weight. His room was functional, and it's not his fault it was hurt by the loss of Nielsen (Okposo too, but mostly Nielsen). The Tavares situation hanging over the head of a till-then unaccountable GM was a massive distraction, but that would affect any room.
If the culture really was so messed up, I don't think it could have improved so much in 1 year with remarkably little roster turnover. The Trotz effect was much more strategic & tactical, but I really don't think his locker room management (beyond the fact that he had Stanley Cup winning clout, which is a big factor) was all that different than Capuano. The shift in team leadership from Nielsen to Lee was definitely compromised by the Tavares distraction. But, again, I don't think you can blame Capuano (or even Weight) for that.