> There can be delivery problems between Gmail and m365 - and even ... - and vice-versa.

Absolutely not on the same scale as 'your' mail-in-a-box toy, though. I'm with OP, even for those who can roll Exim with NixOS or whatever the latest fashion is: mail is not worth the hassle.

I pay Zoho and do/host better things with my time [nearly anything], I have nothing to prove. They [or another provider, not an ad] can fight the mail hegemony; not interested, personally.