But Rome does have seperate animations for different weapons which are not dependant on the model. You actually can give a spear-bearing unit a swordsman animation, it looks weird, but works.
And, for example, the phalanx pike are not attached to the models, you can make any unit a phalanx, just by giving them the attribute. So, it works there. And I think, the unit class "spearman" works similar, though I´m not entirely sure there.