Probably a lot less safe (and harder to aim) if you don't use the truck. Also unlikely they get all the way down unless you mine it in wheel shapes (increasing labor and also, luckily, danger).

Genuinely, I cannot tell what your point is. In some alternate universe, are we just rolling the rocks downhill? Don't you think we'd already be doing that? This seems like a great use case to replace diesel trucks with ones that recharge themselves using potential energy from ore. This absolutely is a galaxy brain moment, in that it's a very smart idea.

Are you surprised by the concept of potential energy?