I'd say if enough people share this sentiment, then there are legitimate problems in self-hosting email. I don't think deliverability is a made up problem. Differing complexities can contribute to one person thinking it's easy, and another knowing it's not.

Both perspectives may be entirely correct, but the devil is in the details. It seems more right to say that in general, self-hosting email is hard, rather than act like it's easy because you figured it out and everyone else running into issues is just inexperienced/dumb/not good enough. Chances are, those folks were dealing with more complexity than you have.