Stravinsky is so far ahead of everyone else in my estimation of 20th century composers that I have a hard time adding anyone to a list consisting of Stravinsky.

If I added to that list, Shostakovich would be on it long before Debussy. Britton, Bartok, and Prokofiev would be on it before Debussy, though I concede that my fondness for Prokofiev is sentimental (that is, his music hits me emotionally) rather than built on strict musical grounds.