Yes, it depends on definitions. If you just look strictly to the protocol, it is different, with different principles, and it does not interoperate natively.
Interoperability comes at a different level.
You can say it is different (yes, it is, of course), but in practice they interoperate.
I do not agree that a bridge is a hack. It is a clever piece of software with lot's of design details.
Multiaccount is good for the closed silos of the corp.web - the open web can be better, with messages going through different protocols with bidirectional interoperability