This is factually inaccurate. It's perhaps true on the Air and base model Pro, but not the others.
I hate on Apple's bs all the time, but it seems like the reality in your situation is that you got nearly the cheapest mac laptop 5 years ago, with a shitty screen, bumped the ram, and you're doing just fine still, except for some esoteric limitations that I just factored into my budget when buying one recently and aren't blocked by, namely external monitor support without MST.
I didn't get that computer at that time because of some of those limitations, sticking with my prior intel 13" until last year, until I finally convinced myself it was time. Doesn't mean they aren't worth complaining about though, I think 5 years on an Air is pretty good, they've always favored mobile utility over stationary excellence