Instead of special gear, they should be able to completely change form with the flick of a few buttons. And since changing classes is already too encumbersome for regular retainers, you should be able to choose their roles before the battles begin.

They could be categorized into types of fighters, that have different abilities that are either superior, or inferior to, other retainers. Or neither.

Oh and wouldn't it be cool if you could put them in the arena and like a real time strategy game, send them after enemy offensive and defensive battlements?

And since we need to strip every ounce of a retainer's identity to make your idea happen while properly balanced, we might as well do this whole thing with minions instead....

On second though, nevermind. I believe I just described Lords of Verminion.