Right now, Devers being forced into the 3b slot is clearly a stall tactic due to personnel. That kid is so thick in the legs and slow on the first step that he will never be defensively average at 3b.
Devers has been improving his defense, so nothing is being "forced."
IMO, his biggest strength is his first step and quick reflexes. I totally disagree with you on that area.
To me, his weakness is in his range, which for 3B is not much of an issue, except when running down pop-ups and foul balls. Fenway's small foul territory, especially down the 3B line in short RF may help hide that drawback.
Note: I've been a big worrier about his defense and have suggested a move to 1B might be best (like when I advocated us signing Moose), but I saw some major improvement on defense, particularly down the stretch. His UZR/150 went from -11.5 to -5.2. If he can get near zero, he will likely stay at 3B, and Chavis may play 1B next year.