I don't understand why you would even make a Fire Emblem mobile game if you don't want to take advantage of the large canvas of characters for gacha. Like, it's fundamentally a bad move to not do it. Anyone arguing against it are people who don't actually play mobile games or at least are not an audience which is worth targeting for such a product and hence don't need to be listened to.
There is no reality in my opinion, where it makes sense for Nintendo, IS, and DeNA, to even consider making a paid premium "proper" (whatever that means) Fire Emblem game for mobile. If they wanted to make a game like that why wouldn't they not just make it for 3DS or Switch? That's where the audience for those games are and they are willing to pay 40-50 dollars or more for it. You won't make MORE money going mobile with a game like that.
Source: I play mobile games.