The most common size of slider buttons has been the same for 100 years. Does that mean it is ideal? Anatomy varies. Methods holding and playing vary. Is it not likely that different buttons might be more suitable for different players? And if so - would it not be wishful offering simple means to change the buttons, being such a crucial part of playing conditions? Replacement reed plates and cover plates have become quite common in later decades. Maybe buttons should come next ?
I think you should write to the harmonica manufacturers about this. Your arguments are correct, but harp players are not the ones you need to convince.
You are right if course and I have approached all manufacturers I know in the matter. But it is bilateral isnt it? Makers act for three reasons…believing they can win a market with some novelty… or…there is an opinion demanding a change…or they fear some competitor is leading the game.
So, after all, I believe some info may be valuable. AND maybe showing some examples what very easily is achievable by some simple DIY trials.
During the last month I have tested half a dozen basic variants on three different instruments and I think a lot can be gained just by choosing some design that suits… 1 finger… 2 fingers… the thumb… the base of a finger…the base of the thumb… or even the palm of the hand. I have tried sizes from 13 to 35 mm…The way you hold the instrument is crucial of course.