A light aircraft will descend faster, so will a heavy one..

[k.swiss]

Please, like I am a five-year-old child can someone explain this.

A heavy aircraft will descend faster because of the momentum it has.

A light aircraft will descend faster because it can reach a higher speed, less limited by VMO/MMO on the descent.

So which one is the truth, do you need to plan more track miles to descend a heavier aircraft or a lighter aircraft?

Additionally in terms of slowing down, which do you need to plan more track miles for? A lighter aircraft will take time to slow down due to its inertia. But a heavier aircraft will also take time to slow down because of its momentum, sometimes you need to drop the gear for example.

Would appreciate any underlying logic. Thank you.