With both the screen brightness and the volume I change them with quick taps to the keys, repeated if necessary. And for whatever reason, they were never hard for me to locate. I'd guess that's partly because they're just 1-2 keys in on both sides. I also suspect peripheral vision helps... I can't "read" symbols on keys (or a touchbar) with PV, but I can absolutely perceive key shapes and so without changing focus I know where they are.

Once I get farther into the row of function keys, I don't have as much of a memory for them. I'd guess that's at least partly because I don't use the key backlight and playback controls as much (auto key backlighting works very well for me, to the point where I almost never adjust it manually, and the playback controls don't work with much software other than iTunes which I've been avoiding for years now). Maybe mostly that, as in the past I've definitely had a "tap without looking" relationship with F5 for reload (now apparently mentally mapped to cmd-R).

"Having a dedicated position to change often-changing settings is more useful" is pretty much the whole point of function keys, except they do a better job of it than the touchbar does, and quite likely a better job than the touchbar can.