Superhuman is a slightly faster GMail, while Hey (https://hey.com/features/) on the other hand seems like a rethinking of the fundamentals of email starting from "Anyone can email you".

I've tried inbox zero etc. but they all fail in the long run for me (I'm one of those folks with the red badge of shame with literally 40,000 unread emails on my phone), so I'm eager to give Hey a try which gives you a workflow of how to do email: screen, reply-later, focus mode bulk reply.