I have considered this, but converting is not risk free. Say I utilize my own domain backed by Gmail. I have increased my surface area by being reliant upon both Google and the security of my domain registrar. Perl.com was just stolen[0] due to some shenanigans -how I would I keep myself immune?
My fear with using my own domain is that if it is compromised, then an attacker can access all of my email linked accounts (eg banking). If Google shuts me down, at least I know the domain is secure and the email is dead and unable to be intercepted.
Banks use 2FA so stealing your email won't steal your account.
Anyway, you can appeal to the registrar and IANA for help if your registration is attacked.