Thomas Shey
Legend
I'd bet money that something like 99% of AD&D as actually played was lighter than AD&D as written. Even Gygax ignored heaps of his own rules when he ran the game. In my experience most AD&D games were a mish-mash of OD&D, B/X, BECMI, and AD&D rules. The first three are all far, far lighter than AD&D proper.
Of course this is true of most rules-heavy games, too; often what makes rules heavy games is not density of commonly used rules that everyone needs to know, but that they take the time to provide rules for situations that may come up rarely or not at all within a given campaign.