No.
Why no? Perhaps his Gaspard might be greater in your opinion, but I think Le Tombeau is his finest work for solo piano.
Huh? His 'La Mer' is 20 times more "greater."
I was thinking in terms of solo piano music. As a rule, I don't care for too much Debussy, but I do like his etudes, and find them very original, worthwhile piano compositions.
You surely can't be serious!
Actually, I am (in terms of piano solo music). A number of his lyric pieces are gorgeous, but the sonata I feel is an underrated work, and is much bigger in structure than most of his other piano solo work.
They pale in comparison to his symphonies.
True. However, I was thinking strictly in terms of piano solo music-actually, I'd probably add the Paganini variations to this list.
Good, yes. Great, not necesserarily "the height of his output."
The Fantasie Espagnole is, in my opinion, Sorabji's most accessible piece of piano music. To tell you the truth, many of his other compositions are certainly mammoth, but I have reservations as to whether they qualify as "great." However, if any of the bigger pieces qualifies, I'd say it's probably his set of transcendental studies (which I now regret leaving out).
Hm, I don't think he meant "just" piano music
You're right, I don't think he did. However, I felt that I should list what came to mind as the greatest piano solo music.