If oD&D was released in '74 and then 5e (probably called something else) was released in ~'78 instead of AD&D, people would probably write a lot of articles about how Gary had heard the criticism of how the oD&D books were inscrutable messes and responded by releasing a completely new/totally-revamped game (instead of how AD&D was seen which, Arneson lawsuit aside, I think everyone saw as a pretty much a re-written and expanded second take on the same concept).AD&D 1st edition, which is more complex than OD&D
Would this game would have attracted more people than AD&D? I'm not sure. Part of me thinks yes -- AD&D, at it's core, doesn't address a lot of problems that oD&D had when the audience shifted from wargamers to college kids and others -- few people like hirelings, fewer 8-12 participant game night, getting to lead armies at name level isn't quite the fighter perk Gary envisioned, combat (without houseruling) is incredibly dangerous yet few people wanted to play the heist game it supposedly incentivized, etc. etc. I think if a game that came along (with the D&D stamp, because clearly D&D/AD&D had a first-to-market advantage) without those issues, it might have been a bigger hit (there would have been some oD&D fans, however, who would be mad at having to re-spend since the games aren't nearly as compatible). Another part thinks no -- simply because 5e isn't that great at dungeon-crawls, and I think bitd before ubiquitous computer games and such, there was quite a market for just exploring and finding out what was behind door #1 and fight things for their treasure and such and TSR D&D IMO does do that game quite a bit better.