This is nonsense.
If the rules are optional, the core game is what you weigh.
But the rules
were not designed to be optional. That's the whole point here. People just CHOSE to ignore them, or never even realized they were there. But they were.
Even apart from that, though: Again, you want to claim that attack matrices, the five saving throws (Paralyze/Poison/Death, Rod/Staff/Wand, Petrify/Polymorph, Breath Weapon, Spell), and indeed the very
concept of "saving throws" in the first place as opposed to just having attacks (they're even named "Attacks" in AD&D1e!), etc. are "rules light"? Or how about THAC0?
Pull the other one. AD&D, and its successors, have NEVER been "rules-light." Ever. Period. Anyone claiming otherwise is either playing sillybuggers with definitions, or genuinely out of touch with what a "rules-light" game is for one reason or another.
Because, as I and others have said, "rules-light" has
paragraph-sized as its low end and "12 printed pages" as a pretty typical size. Even the simplest versions of Basic, which I have bent definitions to allow as possibly maybe kinda-sorta vaguely "rules-light," are four times larger than that--and that's for a
very barebones offering in D&D terms.
AD&D is not, and never has been, "rules-light."