Its ridicoulous to spent 30 pop slots (10 more than euro ones) while both units share stats (or Captured being worse).
They are limited enough at native embassies, just 3 buildings, unlike their counterpart.
Inca, Lakota and Aztecs need number superiority, impossible in this context. Devs could give them the bonus vs walls as unique treat but they give them to everyone, to civs that didnt need it.
Sieging with them is a nightmare, specially on treaty. In my opinion unlocking them at imperial age was the best spot for them.
This kind of changes dont aim players to play these civs 
