I wasn't thinking about the poison archers actually when I made my comment.
Hinnom has ready access to poison ward (Ench4) which would protect it from the poison arrows.
I was thinking of the likes of Oiorpata. They are only slight;y worse than a Van but cost 50G. Fortunately (for other nations) both poison archers and oiorpata are capital only, forcing the Sauromatia player to make a "hard" choice. The Warrior Queen could also cause Hinnom problems and is recruitable everywhere. It is against these troops that Hinnom might find its chariots useful.
Even though I believe that Sauromatia is Hinnom's #1 threat, I believe Hinnom as it stands would still have an edge against Sauromatia (but I could be wrong). The picture might be different if Hinnom's starting army and PD is nerfed.