While I would 100% have been down for a melee combatant Zelda (especially if she were notably different from Link despite that, such as being a more nimble thrusting sword type of person as you suggest) I can see why Nintendo people wouldn't want to go with that. I think if you're innovating in this way, in a series like LoZ, you have to explain why you're doing certain things. If you make Zelda the playable character and she runs around using a sword, the inevitable question is, "Why couldn't this have just been Link? What does playing as Zelda actually change here?"

Personally I don't think you need answers to questions like those, but I think Nintendo does think that.