It's hardly any work at all. If you've made a webview you have icons and splash screens, you have what you need to make the manifest.json.

You can create the simplest of service workers and your done.

If you want better offline ability, you need more TLC in the service worker - which you would need anyway if you want your webview to work offline as well.

The "extra work" takes a few hours. The boons of the PWA over the webview, updates are much much easier to roll out. You don't have a bunch of ancient versions running around. If you don't need access to native APIs this might be worth pushing users to use it.