When athletic height jumping was considered done and perfected, there was the Fosbury flop which opened new possibilities. Do you think there was such a moment in the music history? When someone showed how things can be done and from there everyone is using his/her technique?
Equal temperament, where all the keys have basically the same intervals rather than having different characters as in just intonation. Enabled modulation from one key to another as in Bach and Jazz.
A few modern production techniques come close, but I agree, equal temperament tuning was a game changer. It allowed “anyone” to transpose “any” piece of music into “any” key, broadening the available instruments for a piece.
Plus drop D tuning would be impossible without it.