I'd definitely say they erred on the side of cutting too much if anything. I think the side characters are really critical to the story overall, and it wouldn't be the same to me if they were gutted too much.
Mashiba really did get the short end of the stick though. Same with Shouya's 2 friends from elementary school.
Also there's one scene in the manga
where Shouya and I think Mashiba(maybe? Not 100% sure) go to talk to Shouya's old grade school teacher
and I really wish that scene was actually in the movie.
I didn't do guru this year but
azuarc
can be in my sig anyways.