There's a difference between 'greatest' and 'largest'.
If you are taking away touch, harmony and melody, everything that defines music and makes music beautiful, and simply reducing it to the 'figures', ie. two notes or more, I have no real way of answering the question.
But I would say, you can learn all 26 letters of the alphabet, but if you can't say them properly in a meaningful order, then someone who knows and speaks perfectly with only 24 letters wins the 'greatest' accolade.
Musically speaking, we are adding letters to the alphabet all the time.
Whatever Tatum's inclination or aspirations to play classical, we have hardly any record of it, and as an Afro-American he must have felt frustrated that his career was so limited by his ethnicity. He could obviously play Chopin, Debussey, Massanet, Dvorak.
What record do we have of Cziffra playing a 'vocabulary' other than classical? Does this line of thinking not count?.
Andre Previn was one of the few players who clearly demonstrated he could play various styles.
Regards
Andy