Just a quick thing - as a catch-all for face button glyphs, doing what nintendo does on the switch and doing a little icon of all 4 buttons with the north/south/east/west button highlighted?
No what I mean is basically a bypass to needing to detect, like a glyph that works for any standard gamepad.Basically - just a picture of 4 face buttons in a diamond shape, with the one in question highlighted, that way the image is completely agnostic as to what kind of gamepad you're playing on. this image has some icons for what i'm talking about (check out the 5th row): 
I guess in the long run you could just have it be a preference option too
This was just a quick suggestion as a workaround more than anything, i get that this is all pretty low priority overall, theres still plenty of AAA games that dont even bother