Your argument has less to do with what constitutes a theme park, and more to do with what makes a theme park good.  The Hulk coaster does have a storyline.  You are injected with gamma radiation despite Bruce Banner's warnings while visiting his lab, and you become the Incredible Hulk.  The ride may just be a coaster, but it does have a theme.  It may not be as well thought-out or complete as Animal Kingdom's theme, but IOA is still a theme park.  So are the majority of the Six Flags parks, at least on a basic level.  I would say places like Blackpool Pleasure Beach and Cedar Point are Amusement Parks (though one could argue that CP also has a themed area).