How does any of that show he thought the music of his time was a stinking cesspool of shit as you put it? He started composing as a child and had studied with numerous composers of the day including Haydn by the time he was 20. A couple of years later Wikipedia says "Over the next few years, Beethoven responded to the widespread feeling that he was a successor to the recently deceased Mozart by studying that master's work and writing works with a distinctly Mozartean flavor".
Hmm, sounds like being inspired by a giant in his field to go further, rather than any urge to "replace the stinking cesspools of shit that sully the world, and replace it with beauty".
He certainly may have been cantankerous and touchy, but many great people are, and your own quote gives another good reason - being in constant pain from his abdomen. You also missed the tinnitus he had from his early 20s which made conversations difficult for him. All your quote says is that later in life he supported the Enlightenment and opposed Napoleon. What does that have to do with his career as a composer?
So I see no evidence in favour of your point... I don't usually expect this sort of hyperbole from your points either, they're usually very reasonable.