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?
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.