I agree that the primary factor in creating a responsive player
is the fastidiousness with which the rebuild was effected.  (By
being super-fussy, I once did a single valve Standard Pneumatic
action that could be very easily played with just light pressure
on one pedal, from one finger, so "kicking in" dynamics took
just a little wiggle of the ankle.)

By the end of WW1, most builders seem to have figured out the
dimensional ratios, between the exhaust bellows and the striker
pneumatics in the system, which yielded the most efficient
operation.  Unfortunately, though, the general quality of the
actual piano portion declined after the war, in my opinion.

Gordon Stelter