Changing email providers sounds daunting, but it was relatively painless when I actually committed to it. I did a search over my password manager for my old email and just went through the list logging in and switching to the new email. Probably took a few hours at most.
For anything I missed, I set gmail to forward everything to my new host. Cleaned up the few things I missed, and am only left with spam. I still leave the forwarding rule there in case a personal contact or service I forgot pops up, but it has been years without any issue, and I never feel the need to log into gmail. Certain emails are not forwarded I think, despite the "forward all" rule... but nothing I've ever found to matter.
> Changing email providers sounds daunting, but it was relatively painless
If you have your own custom domain, changing providers is pretty easy, IMO. In fact, the portability factor is probably the best benefit of having your own domain.
> Changing email providers sounds daunting, but it ... Probably took a few hours at most.
That does indeed sound as daunting as I feared, unfortunately.
I want to try another provider, but my family (partner, kids, grandparents) stores pictures in Google Photos, shares docs from google drive, etc. It is all the extra stuff I get with Google that feels daunting to me, I'd love to switch for email and calendar.
As an alternative to forwarding, you can also configure Fastmail to fetch mail from (and send via) Gmail like a mail client.
Did you migrate any old email?
> For anything I missed, I set gmail to forward everything to my new host
This is one of the big reasons I switched to GMail when it was new. Most free alternatives like Yahoo would lock forwarding behind a paywall. A very transparent attempt to keep users by force.
The daunting bit (if you're using gmail or something where you don't own the domain) is getting everyone to update their address books. I took the same approach that you did and it took years before the forwarded emails died down, even with responding to all of them with "please use my new address". I got there in the end, though.
It's a process. I just set up a filter on Fastmail that showed me all mail that was delivered to my @gmail.com address within the last two weeks.
Then I went through that list every now and then, unsubscribing or changing email addresses as they came up. At the moment it's mostly just mail from sites I've used Google OAuth for some reason and can't be bothered to change (or just plain can't - one site actually uses email as a primary key and are completely 100% unable to change it.)