There's not just one "thesis statement" and "argument" for cubist style of art. There's a veritable infinity of approaches you can take here. The traditional stance is that cubist style of art revolutionized European painting and sculpture, and that it was a part of the avant-garde art movement. One less traditional stance would be that cubist style of art was essentially a creative cul de sac that didn't contribute anything lasting to European painting and sculpture.
Here's one thesis statement: "Cubist style of art - a pre-WWII style that still thrives today"
Hope it helps