If they're offering more than one way to do things, and say things like "there's more than one way to do things, and every game is different, try different methods until you find what works for you and your players" then I don't see a problem. Those who've been playing long are, I expect, well aware that the rules can be changed to suit.
Maybe an analogy would help... currently, the DMG (and the 5E rules largely) are like a fill in the blank question. I'd prefer to see a multiple-choice question, with e) come up with your own thing as an option.