Some of this speaks to PG's "Writing to Discover" (http://paulgraham.com/discover.html) observations. When he says, "The paintings made between 1430 and 1500 are still unsurpassed" then my impression is that he's just stating his opinion. But because he doesn't bother to preface it with, "Well this is just my opinion, but..." then it sounds like everything that he says is, as you say, "generalizations based on [his] own tastes, but presented as deep insights about the world".
So because all of his statements aren't prefaced with "sometimes it seems to me" or "I wonder if" or "Maybe it's the case that", then it comes across like he's speaking as if everything he says is absolute truth, whereas a lot of it is simply his musings about the world.
I totally understand why this rubs a lot of people the wrong way. Personally I prefer his current writing style, where he doesn't qualify everything he says with, "in my experience" or "among the artists I've known personally" or whatever.
With that being said, I can't comment on your factual corrections about the history of oil painting.
So because all of his statements aren't prefaced with "sometimes it seems to me" or "I wonder if" or "Maybe it's the case that", then it comes across like he's speaking as if everything he says is absolute truth, whereas a lot of it is simply his musings about the world.
I totally understand why this rubs a lot of people the wrong way. Personally I prefer his current writing style, where he doesn't qualify everything he says with, "in my experience" or "among the artists I've known personally" or whatever.
With that being said, I can't comment on your factual corrections about the history of oil painting.