In fact, it would be interesting to speculate about these ratios in the US. I'm going to throw out these concepts which are just my opinion, to see what the experts have to say. In the US:
1. For people under the age of 60, more people are performing (as opposed to playing) with diatonic button instruments than chromatic button and piano accordions due to the popularity of cajun/zydeco and tex mex.
2. For people over 60, more are performing with piano accordions than any other style.
3. The "niche instruments" (concertina, bayan, cba, diatonic for klezmer or old time, etc.) are found in distinct communities where their performances may outnumber piano accordions.
4. In the future, cba will gain traction over pa as more younger people discover its distinct advantages, especially in jazz.