And...where is Scriabin????!!!
(Sort of joining in the fun here....but in all seriousness....you don’t get to Stravinsky without Scriabin...which is to say, that none of these guys, not one of them, truly, truly, truly, stands on their own. They are unthinkable without all of their predecessors. Such is the nature of the west, with all of its mammoth cultural achievements).
Re: Tchaikovsky. I would wager that the author would say that he didn’t do anything original in terms of harmony to allow him to be among the greats. The real question seems to be then, what is greatness? Does it have to include radical innovation? The author I think says yes...and that is highly debatable, and would be fascinating.
Change the criteria, and Tchaikovsky clearly makes the cut.
What about John Lennon?
I see your Scriabin, and raise you one Buxtehude...