A few comments. IOA is as detailed and themed as anything Disney has done in the states. It does rely too heavily on thrill rides, but the theming is magnificent and by all accounts of anyone who has been there, the theming of Dueling Dragons is by far the best in the park. It is hardly cheesy. I'm very upset that its going away to become a HP theme.
Disney frankly doesn't need HP. Could they have done something better than Universal will? Frankly I don't think they could have. And the fact is that Rowling was being so demanding on how it had to have been built that it would have been a disaster. It seems she's laxed up a bit on her demands with Universal however.
Universal can't compete with WDW not because their parks aren't great, because they are, but because they don't have the size that WDW does. Universal doesn't have the ability to create 4 huge theme parks, 2 water parks, a million hotels, and a dining district but they have done some great things with what they have. Their problem has just been that they've been more of the mentality to build and let it sit than to keep developing.
They have done several things as good if not better than Disney however. Citywalk is a much better layout and design than DTD is. While I truly miss Kong, it was replaced by a superior attraction in The Mummy. BTTF was run down so I'm looking forward to seeing what the Simpsons ride is like. The Horror Makeup show is a fantastic show and MIB is an amazing ride.
IOA also has some great things. In addition to theming on par with anything Disney has done there are some great rides there. Jurassic Park, Spiderman, The Hulk, the entire Seuss area, the wonderful designs of The Lost Continent (which are sadly going away to bring in HP), and one of the best restaurants in any theme park in Mythos.
Are their flaws in their parks? Yes. They need some more dark rides, and IOA needs a lot more family attractions, but they are some very quality parks and any comparison to six flags is as silly as comparing Disney to Six Flags.