In the academic accordion "world" the button accordeon, and in Scandinavia particularly the free bass button accordeon, seems to be dominating over the piano accordion but that is not the main point - "bellows use" definitely - all since the days of 1930s ( Hugo Herrmann and others)- contrary to what you say has had a prominent part. "The folk world" as you say is different (but cajun/zydeco style for instance due to the rhythmical idiom is one exception) and it certainly might be fruitful having more contact or "synthesis" between the academic and folk players concerning development of playing techniques. Counts for all instruments....