I know the other two races have catapult types, but it would also be fitting for trolls, balista is good too. Axe throwers and peon look too short in this picture; especially the peon when you consider trolls are ~ a foot taller than orcs and peons are runts. I've said it before and I'll say it again there is no way jungle trolls would be working with forest trolls, so if I were you I'd change the green trolls to blue. But if you aren't trying to stick to warcraft trolls then it doesn't much matter aside from the fact that you're using warcraft trolls.