Earlier quoted context omitted.
> the key to all my online accounts Most services support primary email/login change
> Most services support primary email/login change They do, but would you like to do that every couple years if, say fastmail or any other service goes out of bussiness? Do you even remember all of them, so you can change the email in time if your provider gives you advance warning that they're shutting down? Long term, it's complicated.
Yes, you have to plan ahead unfortunately until someone comes along and offers an "email address for life" you can forward anywhere.