Eh, no - nowadays most Electron-based apps would opt for a React Native app on iOS, so they can reuse most of the JS logic from their web counterparts. The big players (Slack, Spotify, etc) will introduce native things because it makes sense to, but there's no reason the small players will do this.

Multiple rendering engines in this case also makes sense because the form factor you're designing for is inherently different. As a result, the usability factor comes into play... you're never writing one UI at that point anyway. The point of Electron is that you turn building and testing 3 rendering engines into testing 1.