we can also say in anoother way that gravity has to pull harder on a heavy object than a lighter one in order to speed them both up by the same amount. However, in the real world, we have things like air resistance, which is why sometimes heavy things do fall faster.
However gravity is determined by a number known as the "acceleration of gravity" and on our earth surface it is 9.81 m/s^2 which means within one second velocity will be increased by 9.81 m/s beacuse of gravity. This defines how gravity works.
Although in the reality such things, like air resistance. For example, if you drop a feather and you drop a rock, the rock will land first since the feather is slowed down more by the air. If you did the same thing somewhere where there is no air, the feather and the rock would land at exactly the same time.