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 chords i e Root Fifth Octave on the bottom 3 strings with one barred finger The 6th string is dropped to match the fret of it s octave on the 4th 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