It's a counterargument to a common argument I find incredibly frustrating: that craftsmanship is somehow antithetical to art. Or, to put it another way, that the ineffable qualities of "talent" and "inspiration" are the only things that matter, and therefore skill is nothing. In this line of reasoning, the development of skill is irrelevant at best, or "selling out" at worst, and it's more often considered the latter than the former. As he points out, it's the punk DIY ethic gone wrong: "you don't need to be technically skilled to create" became "you shouldn't be technically skilled to create", with the result that artists/musicians/what have you are scared to learn how to be better at what they do because they're afraid it'll somehow get in the way of their art. Training is "corruption". Not knowing what you're doing is "pure". It's a mess.
Sure, there are a lot of examples of "style without substance", but if the style wasn't there that doesn't mean substance would be. They're not mutually exclusive; they're mutually beneficial. Art made without something to say is empty no matter how well it's put together, but art made without technique may not make its point. It's always better to make decisions based on what works best rather than what you don't know how to do, and that means it's better to have a technique in your toolbox than not, even if it turns out you don't need it for a given work: it's called keeping your options open. To my mind, if you don't care about how your message comes across, then you really don't care that much about your message.
But he says it way better than I can. Check it out.
(I disagree with him about prog rock. But he's allowed to be wrong about some things.)