It's not the only reason, though. Just the thing that solidified the decision to leave. I just came to realize that I was depending on a shady entity for everything. The service I ended up paying for (which is similar to fastmail) can end up failing of course, but it'll take a while and I can always switch to something else once they go into administration. In comparison, I have no idea when or where Google might switch me off, especially since I do a lot of Android and Aurora store tinkering over various devices.

Even if Gmail was 100% reliable it would still make sense to not give them everything about my life. Besides, I also get much needed extra email features out of the change.