Maple is barely heavier than Ash, but also harder.
The main reason that Maple is used by the vast majority of hitters is that it absorbs less energy than ash or birch bats. This makes hitting the ball off the barrel (meaning towards the end or hands) much more painful, but since there is very little give with maple, almost all of the energy in a swing, plus the energy of the pitch coming in, is transferred to the ball in an ideal situation vs. ash which is softer and will absorb some of that energy.
Aka, in theory, the same swing, same barrel, same pitch off a maple bat will have a higher EV compared to an ash bat.