Well, it would be silly to call it 'flawed' in any case, lol. It was/is a game and the only flaw it could possibly have would be "this is not fun." Nobody has ever accused D&D of that (well, maybe they have, but you cannot please everyone). It was really a pretty mind-bending concept. Even at age 11 I was a wargamer. I 'got' games, but when I just HEARD THE IDEA of D&D it was like learning that you are really a Martian, nothing I ever assumed about games in my young life could really be applied anymore. It might not have been TOTALLY revolutionary to a guy like Dave, who was versed in Braunsteins and such, but it sure was eye-opening to the rest of us, probably to Gary too the first time he heard about it. And the thing is, conceptually it seems like such a simple idea too, but it isn't really.
While I think Gary was more of a "document what I did" vs "come up with a set of principles and devise rules around it" sort of game designer, he did have some unique insights of his own. The whole thing about the progression was utterly critical. I've said many times this was the single key reason for the success of D&D over the years. It sucks you in, it invites you to keep trying to attain further levels. Every computer game designer ever knows this paradigm. You can make a good RPG without it, but not one single one of those games has ever been 1/10th as popular as D&D. It takes a lot of savvy to hit on that fundamental mechanic and GET IT EXACTLY RIGHT the first time around. I mean, people can argue about XP charts or whatever, but the basic power curve of 5e is pretty darn similar to OD&D, that says something.