I had this exact experience, I had an email server running on the same ISP for 15 years, got great delivery. I got a new ISP, blacklisted nearly everywhere. IP reputation is super hard and time consuming to build.
So I made the switch to Fastmail, and honestly, it's the best descision I made. Migrating was super simple, and they've been rock-solid for me. I didn't realize how much time I was wasting administrating an email server with one user until I switched.
I spend pretty much zero time administering my server. Once it's set up, it pretty much just runs itself.
The reason I want to run my own server is that I want to run my own spam filter, whose algorithm requires seeing my outgoing mail as well as my incoming. (Though I guess I could do that through IMAP by looking at my SENT folder. But for me it's also just the principle of the thing. I remember the good old days, and I'm not going down without a fight.)
So I made the switch to Fastmail, and honestly, it's the best descision I made. Migrating was super simple, and they've been rock-solid for me. I didn't realize how much time I was wasting administrating an email server with one user until I switched.