The Celtics are currently second in the league in 3P% at 39.1%, behind only OKC who is 39.2%. We have the best EFG% at 57.8%. And the best TS%, actually tied for first with OKC at 61.0%. I am not sure how this all adds up to a team that needs more shooting. The Celtics are the best shooting team in the league by these measures.
On the other hand, we are 13th in offensive rebounding, 1st in DRebs, and 2nd in total rebounds. Of these, I feel the offensive rebounds are the most important. Defensive and total rebounds get increased when your opponent misses more shots. We are 20th in terms of opponents ORebs. I feel the O-rebounding, team and opponent, are a reflection that we do need more size, at least more skilled size. Because we lack this depth, we are "forced" to play small with an extra guard. The team is so good overall, that it doesn't seem to matter, but the "softest" area of the team is depth at big.