I kind of understand your frustration, because it is indeed neither true E2EE (some server holds encryption keys) nor interoperable (you need to use Google service), but let's remember that is it is meant for businesses, not private interpersonal communication. So the goal is not strictly "no one should be able to read this except Alice and Bob", but rather "no one outside Alice's and Bob's organizations can read this message". We all want to live in an ideal world that mails are encrypted using some PGP-style protocol, but as an article points out - this is just nightmare to set up.