Trample would really require a rebalancing. It's quite a significant change to make.
But aside from Trample, which I think is too big a change to even go into here, the siege question...
Didn't we have this discussion before? I took the position that for the sake of realism, a catapult would have no strength of its own (or maybe 5 representing its crew), and some sort of individual bonus in cities. Thus its main purpose would be its siege ability, and it would not be a useful combat unit outside of defending/assaulting cities. Battering Ram should be fast (it's broken down for transport and pulled by horses in a wagon?), have 5 strength, and no bonuses other than its siege capability. That is, if we wanted to try and change siege units to make sense, or be "realistic".