Or maybe they have 10x the experience you do, but it was different experience for reasons beyond their control. Don't over-generalize from a sample of one. That's hubris.
OK, then. They might have 10x the relevant experience that you do, but the outcomes were still different for reasons beyond their control. Better? Your scattershot insult was still full of hubris.
No, that's not better. If the outcomes were different, that's for reasons within their control. That's the whole point of this entire thread! There is no voodoo in self-hosting mail!
You either get everything right (due diligence of your provider and the IPs they're giving you, configuration of your mail server, not sending spam, monitoring your reputation) and your mail is delivered, or you don't and it isn't. That's it. Getting everything right, and knowing what you have to get right, comes with experience.
Or maybe they have 10x the experience you do, but it was different experience for reasons beyond their control. Don't over-generalize from a sample of one. That's hubris.