It is, at least on land units with persians immortals

I think the DE mod managed to have the Xiongnu champion cavalry switch bows and spears but im not sure.

This distinction might be partially due to gameplay limitations, i'm not sure weapon switching was implemented yet. So ranged and melee ships are separated.

It's not about realism, it's about being convincing.   That the world you're playing with is convincing you.   That's why video games are derived from cinema film.  That's why I complain when I see how sometimes the gameplay of the game is about controlling hordes of Greek cavalry.     It's also worth mentioning that you don't risk sacrificing game performance for realism. That's why old games weren't realistic, and the other thing is fun; reality isn't fun.

of course before-after0001-0209.mp4