So I figured out how to make working catapults, siege towers, ballistas, trebuchets, etc, using 3d modeling. After some research on the old naw maps on how they did it, I found out they used 3d modeled parts on armor stands.
They had a certain code when you press shift, 2 blocks next to the armor stand, you'd control it and get specific items on your inventory. These would be items with names such as: aiming left and right, reloading the trebuchet and a fire command. When you shift clicked again, you'd escape the panel and get your old items back.
The turning would work when you pressed the left or right item and it would trigger a command that makes the armor stand move in the direction. The firing animation would trigger a command switching to the orther 3d modeled part with the firing animation.
It sounds pretty complicated but it's actually pretty simple, the coder there figured out how to make it work in one afternoon lol.