I think Prestige Classes were definitely the biggest promoter of 'Builds', since you HAD to meet certain requirements to even take many prestige classes. But it wasn't an original idea. You used to have to earn your way into Bard or Paladin.
1e bard, yes, but not paladin. All you had to do was have a 17 CHA. There was no planning our building for a paladin. And the bard clearly was a Frankenstein afterthought. One reason why it was at the very end of the PHB and not with the rest of the classes. I don't think I even knew anyone who played a bard in 1e, and that covers 1e being my favorite edition from 1981 to 2012. Although in fairness, I did see a bard when 2e came out and it was it's own class from the get go. But I don't recall anyone every playing a 1e bard.