You nailed it at the end, I think!:
Shouldn’t a Mind player be better at donning temporary masks, where a
Heart player would have a more sincerely experienced alter ego/hidden
self?
This confused me for a long time, but I’d say that Heart players’ masks are more like legitimately distinct alternate personalities; personas, if you will. They’re able to compartmentalize different parts of themselves very well–as Dirk puts it, Striders only party “when it’s good and time to party”, so his work and fun personas are very distinct.
Mind players think a lot less about Who They’re Being and a lot more about what they’re thinking. They’re deducers and analysts. If we look to the Persona series for Heart, we might want to look at games like Phoenix Wright or 999 for Mind; affairs where a lot of the drama and tension comes from scrutinizing the logic of a sequence of events, or logic and reasons behind the stated motivations of characters.
Hopefully that makes any sense?
(Thanks a ton, by the way.)

