It's not just power usage but how well apps are optimized for the M1, so some power users are doing well with 8GB with native Mac apps, and even some non-native ones that play well on the M1, and some non-power users aren't because other apps, or even just one app or page, cause more trouble. The Surface no doubt has advantages that way for some of your apps, though at some cost in other ways, as you noticed!
Using an external monitor or scaling your screen may also be factor, if that's what's causing WindowServer to use a fair chunk of your memory. That's more than the usual amount in my experience.
If you want to try to make it work better without spending the extra money, you could try shutting down one program you think might be a problem, see if that works well, and then see if there's a way to adjust settings or use of the problematic program so it fits better. And try different motitor scaling.