I don’t think you necessarily need 1 to 1 equivalent units. You could have some that fill multiple niches or other ways of mitigating enemy siege and buildings.
Universal Siege Units
Rams and Siege Towers make sense for basically all factions. The only problem is that lots of factions would have carried versions instead of wheeled and having unmanned siege would make this look even more ridiculous than it does now. Just making siege crews would make everything look better though.
Battlefield Constructions
More options for battlefield constructions could also be a way for them to level the playing field. Constructable Pyres to create a smokescreen that conceals your units or Mantlets to shield your infantry would let you avoid or tank some damage. Building most siege in the field would also eliminate the need for a siege workshop building. There could be unique options for Maya who had things like pit traps and hornet bombs.
Ranged Anti-Siege
Jungle Archer: Something similar to the Arrow Knight from AoE3. Could be available for Inca, Maya, Aztec, etc. Some of the Incan auxiliary archers apparently used giant arrows. I think they’re referring to tribes like the ones mentioned here:
Skraeling “Ballista”: According to the Norse, the natives had some kind of stick weapon for flinging large projectiles. These could be available to all North American natives. I think there also may also have a connection to Lacrosse.
Tīpao: A Polynesian siege weapon that could be anti-siege and anti-building.
Anti-Personnel Weapons
Bolas Warriors could have an area of effect attack. Mayas had hornet grenades that could also be an option for them.
Anti-Building
Smokescreens could allow rams to get close enough to do damage. Some of the anti-siege units could also double as anti-building.