"He shows his lack of sound literary taste in his enthusiasm for Machen and Dunsany, whom he more or less acknowledged as models".
While I wasn't aware of this Dunsany reference in Wilson, it's thoroughly in keeping with what I wd have expected. The only fantasy author I know of whom Wilson approved was James Branch Cabell, whom he admired for the satirical and salacious parts.
However, it turns out this was not always the case. In an earlier piece on H. L. Mencken , he had taken Mencken to task as someone who "is never tired of celebrating the elegances of such provincial fops as Lord Dunsany, Hergesheimer, and Cabell, who have announced -- it is, I think, Mr. Cabell's phrase -- that they aim to 'write beautifully about beautiful things'." Here Wilson lumps Dunsany and Cabell (and the unknown-to-me Hergesheimer) among the dilettantes unworthy of serious attention.*
The same Dunsany-&-Cabell-among-the-goats attitude holds in the only other reference to Dunsany I've found so far among Wilson's reviews: this time in a 1928 piece on Thornton Wilder. Here he praises Wilder by contrasting him to Dunsany and Cabell: "he [Wilder] has a hardness, a sharpness, that sets him quite apart from our Cabells, our Dunsanys, our Van Vechtens and our George Moores. He has an edge that is peculiar to himself".
So, that Wilson wd disparage Tolkien was entirely in keeping with his decades-long disparagement of fantasy, even as practiced by the greats, like Dunsany and Tolkien. Which makes his changing his mind on Cabell all the more interesting: having attacked him when he was popular, he began to champion him after he'd slipped into obscurity. Partly this was Wilson's contrariness, which grew on him towards the end of his life, and partly it was due to his seeing his role as one who puffed the unjustly neglected and took down a peg those who were being praised more than he felt they deserved.
*Mencken was well-known for promoting Dunsany and played a large part in introducing him to an American audience.