In my mind it has to be done this way because there's absolutely no way you'll recall everything that needs migrating in a short time. Even if you have a password manager as your email is likely older than it, but it's probably a great start if you have that.

Having new email sent to my new inbox would actually be pretty easy for me even, since I've already been renting my own domain for ages now.

It's probably not even several hours of work for me, except that I do want to set that time aside in case something goes wrong and I need to revert things; I can't afford to not receive email anymore.

That, and I do want to transfer all my existing email history.

Changing email providers was easy. But replacing gmail address in all my accounts with my own domain based address took me 2 years to complete. You only have to do it once though, and then you can change providers at will.

This is the way!

Every time google did something to piss me off I moved an account or two in anger. It felt good. It felt so good that when I searched my gmail and only found google-related hits in my password manager, I was slightly disappointed lol