If a rally mechanic is in, it’d be cool if the units could just do it on their own, without a special unit needing to be created, specified, or purposely present by deliberate means of the player. Instead, maybe one random unit in the group that the computer automatically chooses at the right moment can take the temporary symbolic lead for the group and briefly raise a flag or sound a battle horn… and then quickly tuck it away and fight like the rest of them, without any worry that we have to save or protect that particular unit. This would be purely decoration and a formality to let the player know there is some leader, for all intents and purposes, of the group and they’re rallying.
Kind’ve becomes tricky and a can of worms when you try to decide when, where, and how frequently the ‘lead’ unit animation should happen. Would suck if it happened like clockwork for every battle, ad nauseum.
In general, for me, a Captain or General type of unit is better left for Total War franchise, imo. You know, battlefield simulators. I like to think of AoE a little more casual than a medieval battlefield simulator