Maus is not the only comic to have won a Pulitizer. It may be the only comic book to have won the Pulitzer, but even if we use McCloudian definition of "comics" to rule out most editorial cartoons, the 1975 award to Gary Trudeau for Doonesbury would surely count.
And I'd also argue some of the import that you granted Youngblood #1. It's hard for me to see that as the thing that launched the great universe derby, when Image came a couple years after the launch of the Valiant Universe... which took some time to built up steam. Certainly, most of the universes that followed came much more in the Valiant mode, with tightly editorially-organized continuities, with early books contrived to lead to their own equivalent of the Unity crossover. (The Image model was much harder to emulate, as it relied on star power rather than line coherence.) The fact that both Valiant and Image succeeded helped encourage the smaller players, but you know that Comics' Greatest World was already in the works before Image happened.