But back on the topic, I think with less complexity and better marketing, the percentile-based systems could have taken off and knocked the D&D system down. Runequest in 1978. BRP, the core system from Runequest in 1980, Call of Cthulhu, using the BRP system, in 1981
Well, that is a big what-if...
I'm inclined to believe that D&D just had too much headway by then.
And RQ came out with 2 strikes against it right away.
First: While the role under d100 die mechanic may have been more intuitive. RQ then added a lot of complication on top of it that negated any effect it may have had with new players.
Second: Gorlantha. No further explanation necessary...
TSR was pretty good about hitting the supplement treadmill early on. And Chaosium would have had to keep up.
If Chaosium had released something more along the lines of Magic world in '78, with a proper medieval tolkienesque setting, used spent XP instead of skill rolls' for advancement, and kept within shouting distance of D&D with adventures... Things could have gotten
very interesting.
But Chaosium was a Gorlantha vehicle from the start, so the value of such a move is really only visible in hindsight...
in 1981, Rolemaster and Middle Earth Role Playing in 1982, and others. D100 systems were on the rise at the start of the 80's and then what happened? Sure, CoC is still quite popular, the rest just plateaued or sank. Too complex for the early gaming world already used to AD&D.
All of those early games were a reaction trying to address what they perceived as D&D's shortcomings.
The mistake that many of them made was that they were so focused on "Fixing" D&D, that they often neglected to emulate the things that D&D got right.
IMHO it is no accident that it is the lighter rules version of d100 - CoC, that has had the longest legs...