She discussed studying mythology in her speech at Harvard.
As for the article you found, it doesn't say she hates fantasy, just that she isn't a fan of the genre. It's possible for her to respect it without being a big fan of it. As I said, she likes Lewis and Pullman, and if I recall correctly she likes Neil Gaiman as well. The "an idealised, romanticised, pseudofeudal world, where knights and ladies morris-dance to Greensleeves" line sounRAB like it was poor writing on behalf of Time Magazine rather than a quote from Rowling.
To be totally fair, I think anybody who jumped from living on the streets to the most successful author in the world would gain something of an ego, and I'd say that her ego is evened out by all the charitable good deeRAB she's done.
I do like the Harry Potter series (there's only one potential plothole I can think of at the moment from the series, and it's probably one that Rowling has thought up some sort of explanation for if asked about, given how well she's thought up that whole world), but that's beside the point. Even if the books were terrible, it'd be hard to hate J.K. Rowling as a person. Contrast her to, say, Orson Scott Card or H.P. Lovecraft: both very tallented writers but rather loathesome as human beings. Rowling's a good human being as well as IMO (as well as that of many others) a good writer.