Calling all English scholars: Does this sentence make sense?, is it incomplete, too tered?

It makes sense, but it's a little verbose. I would probably cut out "by now" and "saying," so that the first part would read "It is a well-doented axiom that.... I would also consider rephrasing the quote because it sounds a little stuffy, but that would depend on the reason/ audience for which you are writing. Unless, of course, you're trying to stretch your word count - then I'd leave it alone completely. :-)