I can see why Babylon would be seriously unbalanced - instant techs that team members have researched is pretty insane.
Gotta say though, maybe it's just my play style, but Hungary doesn't seem all that OP. They can levy more powerful units, but levies are expensive anyway. They get cheap upgrades for them, but that's still temporary. Maybe it's more useful towards the end when gold becomes largely superfluous, but at the beginning, it seems like it's just making levying a less bad choice. You get envoys.for levying, but given that you have to be suzerain first in order to levy, that seems less helpful to me. Maybe I'm just not getting it with Hungary.