Agreed, I left Fastmail for Proton and am very happy with it. It improves/changes in fits and starts sometimes, but support is always great and overall I am happy with the usability, direction, pricing, etc.
I do wish ProtonMail handled labels/folders as one unified model like GMail does, it's so much simpler and more ergonomic. But I imagine hoping for a data model change like that is probably a pipe dream.
Well you can try Proton for free and see for yourself.
I've noticed that people either care about email being efficient and private, or they care about the comfortable bells and whistles of their existing inbox (and Gmail has many), but you can't really tell which one you are until you test something new for yourself.
I did comparison of Fastmail, Protonmail and Mailfence. Finally, I decided to go ahead with Mailfence due to their end-to-end encryption and stronger privacy focus. I am very happy with Mailfence so far.