Now I'm really curious about those alleged 30% of maps in which you can't effectively use support units but you can move catapults instead. I have personally never experienced them myself. Honestly, feel free to send me a seed of a map in which you can't conquer with rams/towers but you can with catapults. Until then, I'll maintain support units are more efficient than cats 100% of the times, for the reasons stated before.
That's perfectly fine, the AI sucks so bad at moving units that you can win domination without ever building an encampment, even on Pangea (example:
https://www.youtube.com/playlist?list=PL_rvgIlHFK-23CGJxzYWEliwZzvEHfcHS). It's easier if you have some iron, though, because the knight's movement helps a lot. Even having 1 iron is good enough, since you probably won't build the knights, just upgrade them from chariots instead (way faster). Then eventually you'll conquer a few encampments (the AI is bound to build some) in case you ever need them.