I disagree.... but only because I've not been privy to his decline and what he's been getting stroppy about - I'm either blocked from such content or have deliberately muted it because I find some writers a little tedious. His rhetoric on my stuff has stayed pretty much constant for the last few years.
I don't think the site is declining entirely, I think the echo chambers are getting more ferocious and David is everywhere - like a psychopomp of the Great Goddess Algorithmia herself. If he's getting frustrated - there's likely a cause.
Not quite a spirited defence but certainly putting the benefit of doubt his way.