I ran my own mail server for 20+ years, finally giving up a couple years ago. I strongly disagree that it has gotten easier. As the article makes clear, it's a much more complicated world. Things that have happened in the last 20 years include SPF, DKIM, DMARC, and the rise of providers like GMail. And if you really care about owning your bits, in some ways colocating hardware has gotten harder now that VMs are hugely dominant.
The new requirements to be a good mail server are significant work to understand and implement. The feedback loops are also poor: it's hard to know whether you really have them right.
But the real killer for me was opaque major providers like Google. Occasionally, they decided they didn't like my little mail server. I and a number of other sysadmins couldn't find anything wrong with my setup. But mail wouldn't arrive. I even had SRE friends inside Google and they couldn't find out anything; apparently the GMail folks are very secretive.
There are only so many missed business opportunities and disrupted personal relationships I was willing to put up with for my personal taste for running my own servers. Eventually I hit that limit and switched everything over to Fastmail. For me personally, it was a great decision. It's cheaper and more reliable, and never again will I have to get up in the middle of the night to go to a colo. In contrast to my spending a few hours here and there, they have a whole full-time staff sweating deliverability. It's great!
If people think running a mail server is fun, I say go for it. But even there I'd strongly urge them to consider whether "this looks fun" is the right spirit to bring to anything important to their lives, and whether it will stay fun when it breaks at the least convenient time. So maybe keep it fun by using it only for things that don't really matter to you.