My thoughts of Joplin is that his ragtime syncopation innovation would have sounded better if it was merely a single theme within a sonata form movement or wihtin larger classical structure. After all Beethoven's proto-ragtime moment in Piano Sonata No. 32 was merely one variation among the theme and variation structure.
In the end you just have a single short piece of music with a not many harmonic progression. It's a good as a single theme but nothing much more substantial than that