A very large part of that though is Java not being 'generic' over checked exception types. So if you e.g. build something that supports end-user callback code, you need to either throw Exception (accepting all code but losing all signal as to what's possible) or nothing (forcing RuntimeException boxing).

That's Java. And I agree it is a wildly painful and incomplete implementation. I wish we'd stop conflating it with checked exceptions as a language feature.