Funny, the other day I by mistake sent some Spartan (regular) hoplites against a group of AI agrianians who just disembarked on the beach. Agrianians killed almost the whole hoplite unit, in melee...
Sounds like very poor unit balancing to me. In a real-life combat situation, I would venture that in melee combat hoplites would decimate spear-chuckers 99.999% of the time

In the few early Roman battles I have had against hastati wielding AI, my hastati chop up hoplites, no problem.
Player vs AI is a mis-match to begin with, but on a design level I would have a problem with this being the common result. Troop quality, leadership quality, terrain, etc are all factors affecting the outcome, but if per-Marian Hastatii beat mid-grade hoplites consistently 1v1, with no flanking or other outside influences, something is wrong, IMHO.