I've been switched for over a year now, and I check Gmail once every couple weeks now, instead of daily, like I did when I first switched. (I also have a Gmail vacation responder set up to automatically email literally anyone who emails it to tell them I don't check it often and what my new address is.) Yes, I'll probably keep the address forever, but it certainly isn't used much anymore.
Ironically, I had issues with my Gmail address long before I wanted to change providers: My main Google account address has my old last name, and Google's archaic infrastructure[1] for identity provides no way to change it. I had a newer Gmail address forwarding mail to it, because I didn't have a way to move all of my purchases like Android apps and the like, over to my new address' account.
[1]Microsoft has no issue with your account having multiple Microsoft-owned and/or third party email addresses and letting you change the primary one. There's some wonkiness with different services not recognizing your primary email has changed, but largely speaking, this is manageable. I have the same Microsoft account as I had years ago, everything carried over, but now identified by my current email address.
Zoho's webmail is currently much better than RunBox but the latter is undergoing a beta test of a new modern interface.
I don't really want to move to some other service - what I want is the assurance that Google is not going to do something funny with my account or service and unfortunately if they do I will have no recourse.
When I got my Gmail account in 2004 Google was this amazing website that will give away free services and their motto was "Don't Be Evil", at least that was my impression. I still like most of their services, just don't like the "free" deals anymore.