Hahaha. It's kinda funny to see you guys arguing about this as if there were actually an OBJECTIVE way to determine "greatness", whatever that is. Beethoven was greatest because he wrote Moonlight? (eww...) Bach was great because he did counterpoint? (he wasn't the only one to do so, btw) Mozart was great because of the Requiem? (well, can't argue with that)
Why're Bach, Beethoven, and Mozart the greatest, anyway? No one after the classical era?
Anyway, without Bach, there wouldn't BE a Beethoven, or Mozart, or Chopin etc. At least, they probably wouldn't be as great as we know them as now. Yay Bach!