Interesting. I have to admit that I generally consider fractional bitmap scaling to be deficient as well when I see it. But I do have a 15" M3 Air, and it never even occurred to me that it might be fractionally scaled (i.e. it's not readily perceivable for me).
[EDIT] I looked up at settings. Mystery partially resolved: I manually changed the default setting one notch down to get perfect integer scaling, i.e. my Air is running at virtual 1440x932 resolution, which is exactly 1/2 of its native 2880x1864 matrix. The default setting, though, is 1710x1107, which is 19/32. That said, if I set it back to the default, I find that text is too small - probably why I changed it in the first place - but things still look pretty crisp otherwise.
[EDIT] I looked up at settings. Mystery partially resolved: I manually changed the default setting one notch down to get perfect integer scaling, i.e. my Air is running at virtual 1440x932 resolution, which is exactly 1/2 of its native 2880x1864 matrix. The default setting, though, is 1710x1107, which is 19/32. That said, if I set it back to the default, I find that text is too small - probably why I changed it in the first place - but things still look pretty crisp otherwise.