Bear in mind that Ashe has deadeye, making him a very useful archer. That’s basically the main thing he’s got going for him. Both early game, when everyone’s range is limited, and late game when the extra range becomes good for picking off distant key foes (like people with effective weapons, or ballista users).
But having bows/deadeye on a wyvern wouldn’t be a bad thing. Claude shows us how effective it is, and he doesn’t even have deadeye!
if the Wyvern plan is to get in, attack, and canto away - arrows give you a much greater range of movement/retreat. Given Ashe’s general frailness, running away will be part of his plan.
So yeah, I think Wyvern Ashe is a good idea, so long as Maddenning mode still offers the resources to class him as Wyvern while he’s still using his bows as well.