I think the fact that McCoy directed the 7th best overall offense with the horrible OL and insane amount of injuries SD had last year is an absolute testament to how great a play caller he is.
Ron Leary is an above average guard, not my own opinion, but that's what Pro Football Focus grades him at.
Bolles was considered the best and most ready to play tackle in the draft.
Okung was the 38th rated OT by PFF last year, so it's not like they lost Orlando Pace in his prime.
They are very weak at RB, that I can see being a major weakness all year.