Greatness is defined by extreme and unusual talent combined with lasting cultural impact. With respect to the composers you mentioned, their cultural impact has

Greatness is defined by extreme and unusual talent combined with lasting cultural impact. With respect to the composers you mentioned, their cultural impact has been tiny - in the sense that their influence on current and future composers and audiences is likely to be negligible. There's a point at which a medium becomes stale no matter what you do with it. No one declaims epic poetry from memory or writes complex medieval polyphonic vocal music now, and IMO orchestral/classical music is going the same way. Bach to (roughly) Berg's opera Wozzeck will keep being played, and perhaps Reich and Glass from the 60s/70s. But I'm not hearing much else that has broad non-niche impact and appeal.