No support for IMAP or SMTP is a dealbreaker for me.
They have a bridge application you can run on you computer to use with local mail clients. I understand the reasoning for not having it normally, but it is rather annoying.
ProtonMail doesn’t support email export, or at least didn’t a few years ago when I switched to fastmail
ProtonMail's spam filtering is subpar to most of the other suggestions here. The UX isn't that great and the apps are crap. Good/reliable email service though.