2020 M1 air - one click down is crystal clear.
That's because one click down from default on the 2020 MBA is 2x scaling.
The
default on the 2021 MPB is 2x scaling.
The 2021 MBP has higher ppi (254 ppi) than the 2020 MBA/MPB (227 ppi).
For best sharpness, use 2x scaling.
Most people cannot tell the sharpness isn't quite as good when scaling other than 2x; only those with a very critical eye can tell. Apparently you are one of the latter. The difference in sharpness should be very slight.
If this is not acceptable to you, and you do not like using the default (2x) scaling on the 2021 MPBs, then maybe the higher ppi screens of the 2021 MBPs are not for you.
One possible workaround is to hit Command + (i.e., the shortcut for zoom in) in most apps to enlarge the text (but it is not the same thing, and only works for some content and some apps)