Two Sets of Rules, the Good and Bad?

[JNAProductions]

I don't see a distinction between that perspective and "arguing that a DM should never use PHB rules for NPCs". What difference do you see?

They're not using "Should" as a moral thing. They're using it as a practical thing.

Put another way, when you want to cut the beef you just cooked, do you use a knife, or do you use a laser? Both work just fine (assuming a sufficiently powerful laser) but one is a lot more practical, convenient, and easy.