Do you have an example of that? It's a pretty niche topic to decide he was being curmudgeonly. A lot of people think that about modern art whether they're wrong or not they're usually pretty normal people.
You mean Not Banksy the pretend street artist, or Not Not Banksy the pretend commercial street artist, or Mr. Brainwash?
But how does someone read that as a criticism of modern art (whatever that is) and not Watterson resisting the commercialization of his work?
That isn't one of the strips I was referring to, and that one is mid-period Watterson and not late-period Watterson anyway. But since my original post got the reception it did here, I am not going to dig through the archive to find the ones I meant.
I was asking for the ones he was thinking of when making his case about Waterson. The one you linked for example does not seem very harsh to me so I'd assume he wasn't referring to that one. I can't know that without him providing it directly.