Thanks for pointing those people and their thoughts out Barry. You are absolutely right. I have known so many violists personally and can honestly say that they are humble, dedicated musicians who's ego's are not as big as violinists. They are often violinists who decided that they prefer playing the inner parts and prefer the ability to play darker deeper richer tones. My experience has shown that they are organized, proper and lovable. The viola jokes exist not only because they exist with all instruments but because violists themselves have a great sense of humor and are the biggest viola joke tellers of them all.
It seems opinion could be divided over what criterion to use, it could be argued that Bach, Mozart and Beethoven were the three best violists of all time (fortunately there are no recordings of them playing, so anyone who wants to argue cannot actually adduce much evidence one way or the other).
I don't remember exactly where I read that each of Bach Mozart and Beethoven played the viola, it was probably on the internet somewhere, and I think in more than one place. Alternatively, Lionel Tertis may mention it in his autobiography, or Barrett in "The Viola" or Dojeski in "Modern Viola Technique". B M & B should have all played the cello and violin also, and harpsichord, clavichord, organ, and (in the cases of Mozart and Beethoven) piano. But I have not checked that they played those instruments.
What I read was usually couched in terms of in ensemble string performances they each habitually chose a viola (when they presumably had the choice of violin, viola and cello). Maybe they did it to fill in out of necessity where other musicians (for reasons of financial security) would not touch the poor humble lesser viola, assuming that when musicians played for a living, a viola was a bad career choice ? (And probably still is.)
For my part I would suborn the central allegation and then couch it in terms of "the viola is not competitive, whereas violins are a competitive instrument". Next I would extrapolate from a person playing a viola by choice that the person did not feel that they had to prove anything (and did not have to compete - a problem with competing is that it can leave someone as second - third - fourth best or as a loser or as a second violin).
Maybe it is one of the internet pranks or myths, something put out by insubordinate or subversive violistas/violists to confound violinists. And that is one reason why I spread the myth. A second reason is that I prefer the voice or timbre of a viola. The timbre is a subjective quality, so it is only my personal taste that a viola sounds better.
I have no evidence that B M & B were virtuoso violists, and no evidence that they weren't. They were pretty good at composing music though, which is rather more important in the wider scheme of things than being a good violist. To put them in the top 6 violist category defeats my pre-conception of a violist as a helper rather than as a leader.