> What an I missing?

The contractual requirements that ICANN imposes upon registrars. They can’t just take your domain for any old reason. The rules are fairly well defined and registrars can lose their accreditation if they do not follow them.

https://www.icann.org/en/contracted-parties/accredited-regis...

You probably won't get hacked and have your domain taken down for distributing malware. But you also probably won't be randomly banned by Google/Proton. Neither feels like "full, unbannable control of my email" to me. If anything, I'm more concerned about my little old domain getting hijacked than getting banned from a hosted email account.

You aren't missing much only that domains are a bit more portable between registrars and they've historically been a bit more resistant against random bannings.