How would you prevent that, everyone only uses a well known email provider domain that doesn't recycle addresses?

If someone takes over a domain they can also get https certificates, reset all their passwords and do all kinds of other things that are related to it if there's no second factor. That's just what you have to accept if you don't renew a domain.

Fairly recently there was a story about somebody getting locked out of their gsuite account because their domain dns was hacked (IIRC) so a custom domain also introduces an additional attack vector.

It's not the same thing, because by paying for it you have a binding contract and can switch providers too. If you don't pay for it, then you don't have a claim on that email address, as the terms of use can change at a moment's notice.

If paying for it is a problem, then pay it in advance for 10 years and setup automatic renewal. Also leave a digital will. You probably want to do that anyway.

How is that not the same thing as paying for an email account with fastmail?

In terms of the binding agreement, it isn't any different, except you can can move to different providers whereas if you don't own that domain, the service provider has you by the balls.

I use my own domains but if those expire someone else can gain access to my email? Don't forget that domain names can be valuable and may need to get sold if someone bids high enough.

So you mean to say "email done your own uncompromising way"?