This sentence should be read closely if you're considering running your own mail server. Each point listed is a sophisticated technical topic.
So far no problems delivering to Gmail. I was initially junked by Outlook, but that fixed itself after a while since I had sent enough emails to build up reputation.
For me, Google has been really relaxed in terms of receiving mail from selfhosted services in the past. Stopped using gmail for monitoring stuff a few years ago, but up until then, every single cron job / monitoring mail was delivered into my gmail inbox. Outlook is another story. They may just throw your mail away without even a bounce. Had to deal with that several times at $PREVIOUS_JOB.
I am considering self hosting but this would mean I would have deliverability issues with around 90% of my messages.
I also tried to run my own mail server for years and I also had major issues delivering mail to Gmail and Outlook. Because of this I would never recommend self-hosting email to anybody else. Somehow you have my exact experience and your reaction to it is the complete opposite of my reaction. Weird.