I am pretty sure EB slingers get a bonus vs armour, I think that is one of their attributes. The Armoured Elephants are spaced out too much, I think only Seleucia and Carthage can train them. I know I found the Merc Hoplites, I have seen them in Tribus Sakae, and somewhere else. I know I used them as Parthia, and I never got out of the main starting regions.