It makes sense but maybe more to it than that. It's early and I love Brad Stevens, but how does the coach everyone loves for his X's and O's acumen have a team with that much talent rank 24th in OEff and Luke Walton, whose schemes get ridiculed, have his team (with Bron + guys everyone says don't fit) ranked 11th?
For whatever reason the Celtics are struggling on offense, some of it is Irving missing time last year and of course Hayward slowly getting back into form, their defense has been carrying them, I'm sure at some point they'll figure it out. Last season they were 18th in offensive efficiency but 1st in defensive efficiency, so Stevens is a coach who stresses defense. Jaylen Brown is shooting 38% from the field, Hayward 40%, Horford 44%, Tatum 39%, Rozier 35%. I have to think those numbers will improve as the season goes on, but unlike the majority of teams who try to outscore the opposition, the Celtics are still playing an old school type of game where defense wins games, and they're one of the best defensive teams again this year, they'll be fine, they have too much talent to have a mediocre record all season.