I don't know if the chance is equal, maybe if the signer app is very small and does only one thing and is very hardened and doesn't change all the time that does lower its chances of having an exploit, but in any difference isn't that big, so I wouldn't sell that as a silver bullet.

What makes more sense to me is the idea of having your key in one app, you confine your trust to that one only, and use it to sign events from a bunch of different single-purpose apps, which is my ideal for Nostr (and the opposite of Amethyst's ideal, which is to have inside itself all functionality of any app ever dreamt by a human).

Since Wisp is already positioned as the keeper of people's keys, it would make sense to allow people to host a bunker or a NIP-55 signer in it, in case they wanted to use other apps while leaving their keys inside Wisp.