Switched to Fastmail many years ago when self hosting became too time consuming for me. Never looked back. I had to use their support only very occasionally and even then their reaction time and competence were outstanding.
They do just one thing - email - and do that very, very well.
Yes, I use their calendar web app on Desktop (the one next to Mail). For mobile, I sync individual calendars into my Android Calendar ("CalDAV-Sync").
My biggest issue with the Google Calendar was the syncing rate of 24 hours for iCal feeds. On Fastmail, new events appear quite fast (and I can force the update manually, if I need to).
This seems like a really common use case that ought to work well. I switched to Fastmail a few months ago (I still haven't fully committed to sticking with it.)
Did you contact support?
Did you solve the problem by switching to another calendar provider?
I use their calendar with various apps like Fantastical or Timepage. It's standard CalDAV and should work with any decent calendar app, including defaults like Apple calendar.app.
They do just one thing - email - and do that very, very well.