Taking Ness to Pirate Ship would be an hilariously poor decision for Marth.
Also it's easy to avoid the walls on those stages, and the stock loss isn't "instant" in the unlikely event you get grabbed near one; in fact it's quite slow and drawn out, so the stage might end up changing anyway.
Not saying you should. Just saying it's possible. I was more pointing out stages with temporary walls at that point.
And if your the least bit competent and can do the grab release against a wall (I'm not talking about getting into position), it's a huge disadvantage. For example, pk stadium, you can't seriously expect to not be up against walls at some point. Even if the stage changes before Marth can get to a killing percent, Marth can seriously hurt Ness's chances of winning. Not to mention, Marth already controls the match, all it does is limit Ness's options more. That's all I'm saying. Don't take instant so literally. Besides, we've already established if Marth doesn't have a wall to do it against, he can do it until Ness double stick DI's out and then he gets a tipper fsmash to the face. Yay face!
I mean tipper fsmash.