I was actually agreeing with you, in that running a private mail server is not a difficult endeavor as long as you take those things into account. Most VPS and CSP will block SMTP by default (just recently went through this with AWS, had to specifically request the service) since most everyone doesn’t have a clue how to secure mail relays and stay off blacklists.
Google, Live, AOL, Yahoo etc might hassle you for DKIM or SPF, but in my experience the ISP is the first hurdle.