In my 6+ years of being forced to use Office 365 for one of my accounts - it is a flaming POS. Plagued by poor performance, regular (unexplained!) outages and has series issues with data consistency and don’t even get me started on it’s terrible rules system.
Let's not forget that with slightly more money that Fastmail or Protonmail are asking for just one mailbox, MSFT is offering you a whole office suit plus 1TB of storage.
Your criticism regarding functionality might be true, but there is no reason for competitors to charge more.
I'm just a simple email user -- 50 emails per week -- and I don't keep them in my inbox. As soon as I'm done with them, I delete them. A simple 50MB inbox is sufficient for me. I just need an ad-less mail box. For me anything beyond 5$/year is expensive as hell.