I already posted that I recommend fastmail elsewhere in this thread, but you raised so many good points that it reminded me of some extra points :)

Fastmail offers granular, per-app passwords – I have a single password which has read-only access to IMAP in order to back up all the data on a timer. This feature is missing from many (many) other email providers - using the 80/20 rule, if they even offer it it’s a single password with full access (Mailfence, for example)

Since this community is about selfhosting I think it's worth pointing out that this is AMAZING for selfhosting. I have all me selfhosted services sending e-mail via fastmail's SMTP. With per-app passwords I don't need to store my normal e-mail password and the apps can be limited to SMTP only (so no read access). And in case of compromise you can revoke permissions on a per-app granularity.

Fastmail offers full CardDAV (contacts) and CalDAV (calendar) access, which makes plugging it into any other app that supports this very easy - their DNS wizard helps you set up the service records. I use “DavX5” on my Android to sync all Contacts and Calendar outside of using the Fastmail app (which is a self contained app on Android, it’s not too bad)

Fastmail has become my contacts app now - it's really great to have all your e-mail and contacts in the same place. The contacts don't even need to have an e-mail address - I have a lot of contacts stored for whom I only have a phone number. I sync to android using the same DavX5 app and then immediately have these contacts in whatsapp and signal.