The huge cap increase has hurt badly.
Pretty much everybody now has space to add a max contract guy over next 2-3 years. Far more competition for Boston to deal with and almost all of those teams already have more high level talent on their roster than this Celtics team does.
Plus, with the cap about to spike up, it is near-impossible to overpay for quasi-star FAs this summer because all those deals will range between reasonable to bargains once the cap goes up so it's extremely difficult to pry away any of those restricted FAs.