Potter may have been mediocre, but it did breathe new life into fantasy the way Star Wars helped sci-fi. I doubt we'd have had the wide spectrum of fantasy available today if she hadn't published it.
Love it, hate it, or just plain don't care... I don't believe HP has contributed in any way to a "wider spectrum of fantasy available." Brought more young readers to the fantasy genre? Certainly. No doubt about it. And that's no small achievement. But it didn't do anything to increase or affect the variety
of fantasy available in the genre. All the various fantasy tropes and subgenres were pretty much the same post-HP as they were pre-HP. No new ground broken.
So while it may seem annoying to some that things that are popular tend to automatically get dissed... I find it equally annoying when things that are popular get attributed with lofty achievements beyond their popularity. Isn't it enough that you enjoyed it? It should be.