Seems to me that the "button boys" might have an advantage in coordination - in that they don't need as much.

Flatpicked or fingerpicked guitar/mandolin/banjo and whistles, they all need coordination between the two hands for a single note. Violins need coordination on changing bow direction (which is also a matter of phrasing), but you can do several notes very quickly in a single bow and only your left hand is active in changing notes. Similarly, top electric guitarists can play ultra-fast by using sweep picking to hold a single shape with the left hand and produce an arpeggio in one "sweep" across the strings, or by using two-hand tapping to minimise/eliminate picking. Button/piano accordians and melodeons, and pianos for that matter, need no coordination between hands beyond what's required to play several notes together.

Also there's the question of pure inertia involved. Playing a concertina fast will always be a challenge, because there are some notes you can only get in one direction, and changing direction quickly on that is going to be hard because of the mass involved. Guitarists might use lighter strings to minimise the finger pressure needed, if that reduces a tendency to stiffen up on the left hand. Some players with stronger fingers might even use *heavier* strings because the extra upward force helps them leave the frets faster when you lift your fingers off.

But ultimately I think skill's got to have more of an impact. A good player on a "harder" instrument will always beat hell out of an average player on an "easy" instrument.

Graham.