A tier system makes sense - obviously, how much someone pays is proportional to how much time you can put into it. And time = detail, stands to reason.
For learning PBR in a practical way I would recommend grabbing the dDo public beta. All the included materials are scanned with the correct values and are good as a reference, if nothing else. But also, it will let you texture assets insanely fast and produces much better results than Substance Designer in my experience. As an example, everything I’ve made for Grindstone so far was textured in a few hours. The only downside is it’s a bit buggy with the Unreal Engine workflow (i.e. using Metalness), but they’re working on it.