I get your point and in the context of selfhosted it makes lots of sense. But I wouldn't write of postfix, its included with all the linux distros, in a lot of them as a default mailserver. And would strongly argue that it still has its place, even though its configuration isn't beginner friendly. Kinda like a crocodile, it hasn't changed much in all those years, but maybe it didn't have to.

A VPS doesn't protect you from configuration mistakes.

This makes no sense. Postfix supports auth, since forever, with varius mechanisms. What is a modern mailserver in your opinion? Honestly curious.