replacement driver wont do anything this light is already almost DD
the many resistances on all those parts simply eat up the battery voltage, also the battery itself drops in voltage under load a lot

here an example of a Samsung 30Q vs some Ultrafire cell
at 0.2A the UF cell seems acceptable in capacity
but at only 3A this changes dramatically the UF cell barely drops to like no capacity

on a flashlight this means the voltage drop results in a massive drop in current, this explains that the light does not get hot
those cheap lights are depending often on a crappy battery to stay within a current that does not kill the LED