Philip Hensher in The Spectator wonders about Debussy being apparently devoid of influences:
Hardly anything in Debussy’s work is obviously indebted to a predecessor. The hunt for influences on him is a favourite game of musicologists because it is so perverse; once you have mentioned Mussorgsky in the first orchestral nocturne and Wagner’s Parsifal in Jeux, there is surprisingly little else to add. Indeed, there is a good case for calling Debussy the most perfectly original composer of the past 200 years.
One exception is that ‘The Sunken Cathedral’ is obviously inspired very strongly by Satie’s ‘Ogives’ (and we know that Debussy admired Satie and considered him a game-changing composer). I searched around for a written expression of this a while ago, and couldn’t find anything, although I’m sure I remember some acknowledgement of it in my Conservatorium days.
If you like this sort of music, have a listen to both of them: