Battling hordes of different enemies, something you don't do in Breath of the Wild, is a little absurd, I feel. There's a memory in BotW where it's shown that Link kicked ass of lots of enemies, and Zelda is healing him, so I guess it's not that out of place.
I don't feel like it is out of place at all, i actually feel like a prequel couldn't have been told properly without the musou or beat em all type of game. It is referred to as the "Calamity War" and Botw was post appocalyptic. Monster camps and remaining villages were placed a distance form each other cause everything else was destroyed. We just explore the remains of the world and the monsters that remain alive after the great battle.
As for people saying they won't play this because it's a musou, i do feel like this will be a lot different. Seems like it will be limited in the playable options and it will be story focused. They seem to really be willing to make this something special not just a random musou game or else the Zelda team wouldn't be working on it as well. But eh, maybe i'm wrong. We will def see gameplay in 2 weeks on the 26th so we don't have to wait very long actually.