Are we experiencing lower level of gravity now compared to past?
Earth's radius is about 6400 kilometres. That's 6400000 metres. Let's say that you have a mound 20 metres high, burying an older settlement. Your new "radius" is now 6400020 metres.

Let's say that $g = 9.8\ \rm m/s^2$ at 6400, your new gravity will be $g = 9.799939\ \rm m/s^2$.

Clearly, this is hardly "lower level of gravity".

To make this even less significant, the 20 metres of extra dirt underneath you have their own contribution to the gravity. Even though the overall mass of the Earth is the same, local mass variations cause gravity anomalies. Not much, but $g$ changes by a bit. So adding more dirt directly underneath you will increase $g$, counteracting the fact that you're 20 metres farther away from the centre.