It was a ton of effort, and I started because they kept breaking / discontinuing things I relied on. I finished because of privacy concerns. I see no evidence that they are addressing either of these issues.

I’d guess when they lose a user, it is usually permanent.

Less anectdotally, DDG’s adoption curve looks solid:

https://duckduckgo.com/traffic

Also, the gmail client seems to have peaked in popularity:

https://emailclientmarketshare.com/

and services like fastmail are more popular:

https://trends.builtwith.com/mx/FastMail

(Be sure “all internet” is selected to see the recent uptick in presumably personal email hosting)