-The problem lies with the materials already piled up for each object added, and there's no deletion of these once the object is removed????
-Besides, the problem is justified because loading an object map, for example, will call up far too many identical materials for each UV.
-The game's polygons collide, and the hidden parts represent far too many. I select "on Blender, for example, when the meshes are under the ground." The same goes for the grass, you'll see some underwater...
-The landscape lowers your FPS because it's not automatically generated... yet it's easy to do?
While chatting a long time ago, I already mentioned the problem with materials; it's been reviewed... but
The idea of having inertia parameters is also interesting.