I used a laptop running Lion well into 2015, and after that a laptop running El Capitan up until late last fall. They were both at the point of no longer receiving security updates, but they still had supported modern web browsers (Firefox) and apart from Homebrew being a pain about older OSes, they did everything I needed them to do and got me through an undergrad, a master’s, and a number of freelance programming gigs.I also remember how fast my MacBook early 2008 became obsolete. No software even supports Lion anymore (the last supported OS on that MacBook) and also even High Sierra is becoming obsolete.
I don't understand his logic. Of course you have to upgrade when possible.
Of course I’ve also been a PowerPC Mac nerd for ages, so I’m used to working around incompatibilities with older macOS versions 🙂