"So why was this recommended, and defacto mandated, for that age group, again?"
Because by preventing cases or even just reducing the virus load, it decreases the likelihood of spreading the virus to others.
Yes, the guy is legendary in terms of maximum arrogance. He did impressive work early on designing a complex system, but gets defensive when that overengineered moloch runs into real-world problems. Systemd has accumulated lots of small hacks to make it more versatile, let's hope a better solution will be available one day.