Debussy was definitely a terror and gave his professors at the conservatory apoplexy. Nonetheless they knew he had high potential and saw fit to award him the prestigious Prix de Rome which furthered his development. In the years after Liszt, there can be no question that the next big wave of innovation in composing was Debussy. Marguerite Long studied all of Debussy's output with him, he often demonstrated at the piano, and she thought he was a marvelous pianist too.
By the way, similar to Rachmaninoff, Debussy wrote a whole book of songs. And his being a pianist, the accompaniments are everything you would want and expect from Debussy. I remember doing "Beau Soir" with a soprano in recital. It was fabulous!