Drop D is not as significant as you believe it to be nor is it entirely different from standard tuning Drop D is merely a method for playing power chordsie RootFifthOctave on the bottom  strings with one barred finger The th string is dropped to match the fret of its octave on the th string while the tuning of the other five strings remain the same as standard Considering Drop D tuning was popular long before Tool was formed and it was hardly what the band has evolved around