I'm not going to be one of those people who tries to convince you to stay, but my personal feeling is that you're blowing some small things out of proportion. I haven't notice an outage of any significance for
years. Well... you have your experience.
In truth, FM could be pretty bad in the early days... say up to about 2010. Some of us stuck it out for years because we liked a lot of features that couldn't be found elsewhere. This is still true.
But also true: I have found the service to be extremely robust and stable for 10+ years now. Now I've got the features that I love and a mature company and team providing it. I was SOOO thankful when they separated from Opera. Nothing not to love now except the occasional minor irritation of minor UI features changed without my approval
I'm not a super heavy user - just (I think) a normal casual user who spends an hour at most on email per day. Maybe that makes the difference in our divergent experiences?