As much as I enjoy the heritage of Linux theming, I do have to agree with you. A lot of it comes down to a difference in HIG, and as you've suggested, the quality of a theme mostly comes down to how well it works with those constraints. Normally I'm pretty unimpressed (those Big Sur themes have a real chicken-and-egg feel to them), but the few themes that I've seen that go out of their way to make a good, Mac-like experience are Nordic[0] (my personal fav and daily driver), Prof [1], and Juno [2].
[0] https://www.gnome-look.org/p/1267246/
[1] https://www.gnome-look.org/p/1334194/
[2] https://www.gnome-look.org/p/1280977/