Roll Acceleration = Roll Moment / Roll Inertia
Roll Moment: produced by ailerons, limited by wing flex (especially high aspect) and local maximum lift coefficient. More span adds more Rolling moment as the lever arm increases.
Roll Inertia: the mass multiplied by its distance to the roll axis. It will increase much faster than the roll acceleration of the aileron.
Now, roll acceleration creates roll rate. Roll rate is damped by roll damping (master of the obvious). And again, roll damping is function of span. The induced vertical velocity at the wing creates a different local angle of attack that opposes the roll direction. Upward wing will see "air flowing downward", thus lowering local angle of attack and creating a damping. That's why roll rate is so excellently damped on basically all aircraft, except maybe a flat-spinning Starfighter.