The form of 'Ragtime is hardly American. It echos the layout of Brass Band medleys (I shouldn't dignify that 'form' any further, perhaps), and is about as organised as peering into a photo album that has pictures taken by eight photographers, living in eight different countries, and taken over a period of 200 years.
Ragtime, to me, has always been thought of as shallow, cheap, ingratiating froth. Melodically shallow, and harmonically simplistic, at least 200 years behind what was happening in Europe etc.
Then, quite by chance, I heard a very old recording of Joplin playing his music. "Solace" It was exquisite, sensitive piano playing, and the music was far less disorganised than I expected. It was captivating!
Maple Leaf Rag begins with pointless clanging, but it redeems itself with magnificent polyphonic rhythmic interplays soon, before disintegrating a la Brass Band Medley. Hardly great music, but Joplin's delicate playing still captured my attention.
Like Australia's Percy Grainger, Joplin never tried to be avant guarde, but his quality of redemption is his delightful mastery of the piano, and his ability to charm without any pretence of profundity or genius.
EDIT... If one chooses to paint what is often called 'cheesecake' in an effort to be popular as an 'artist', it is manifestly stupid to be offended when one's name is not listed alongside that of Picasso! Many American composers, living in a community that tends to judge success in terms of money earned, seem to be a little put out when the world outside the USA dismisses their output with a degree of disdain.
Joplin, to me, is a talented musician who conformed to the mores of the country in which he lived. He entertained those around him. This, furthermore, he did very, very well. But he lived at the time of Schoenberg, of Debussy, of Webern. Only a blindly patriotic American would feel hurt that Joplin is not mentiuoned alongside them.