I find the idea that all comics are nothing but sub standard visual art ludicrous. First off there are many different styles of comics from the simple "meat and potatoes" art style of well known and loved comics like Peanuts and Dilbert. To the surprisingly detailed work of artists like Jim Lee of Batman. And who are we to judge what art is sub standard and what is a masterpiece. Just because some comics have simplified images or caricatures does not mean that the artwork is any better or worse than pieces done by artists in other genre's of art.
A lot of the art found in comics and graphic novels can often be surprisingly detailed and masterful pieces of art, some examples include as i mentioned above the work of Jim Lee on batman and superman comics and Alex Ross who has done work for both Marvel DC and his own original comics.
Of course there are comic books that have been made that you wouldn't consider to have especially impressive images in them. But putting down the entire genre because some of the comics don't have amazingly detailed painted images in them is ridiculous.