I would argue that's not true at all. A beautifully composed sentence of trite nonsense is still just trite nonsense. For writing of great beauty to become a matter of great consequence, the pith of it must be seen as consequential.
I'm not a fan of art for art's sake. If the artist is unwilling or unable to talk to me on the substantive level that I demand, then I can't praise the artist except in the most superficial way. That said, superficially, Nabokov is a great artist.
Nabokov disliked the phrase ‘Art for Art’s sake’ since most of the people who used it like Oscar Wilde were actually ‘rank moralists’. Anyway, as I decribed ealier, he did deal with important issues. Read his ‘Lectures on Literature’ on writers like Austen , Dickens, Proust, Tolstoy. It’s illuminating.