“RPGPundit” is not a respectable figure, he’s a lying, racist ass. Don’t waste your time on his vitriol. I have plenty of other complaints about Gary Gygax, but they’re not relevant here.
Jeffro’s post is correct about AD&D, which was intended to be a fixed system like Chess, with no variation possible for tournament play, the only thing Gary Gygax did at that time. (Also distinguishing it from OD&D let him rip off Dave Arneson, the real creator of the game… Oh right relevant)
So play OD&D or really anything other than AD&D if you like freeform gaming. That’s all there is to it.
OK, that’s a whole blog post of a rant there, and not at all relevant. OD&D was a mess, but it’s unambiguously freeform, you are repeatedly told to make the game yours, not that you need permission.
OD&D got a good rewrite, by Eric Holmes and later Tom Moldvay. Both are blatant about freeform play.
The one place it looks anything like “rule zero” in AD&D is that afterword, where he tells you to consider: 1. The game as a whole meaning tournaments and West Marches style cross-table compatibility, 2. Your campaign meaning don’t fuck with the balance, 3. Filthy peasant players last.
Gary’s strident editorials in Dragon were clear, you can’t “barracks lawyer” as he put it, out of “you have no rights in AD&D”.