Where do you get the idea that tourist destinations in one location, don't compete with those in another?
First, WDW has never been in the day park/local market. This would be a completely new market, one that I don't know can be profitable. You are going to have a huge initial investment, in land, infrastructure, build out costs, but you are NOT going to be able to charge WDW or DL prices. There is a reason you don't see a ton of local park new construction as opposed to taking over existing parks and building them out.
Second, if WDW presses its one major advantage over other them park operators, its huge IP library, you will absolutely get canabalism of attendees from the costs. If families in the Midwest can get a similar or close to it experience visiting this Texas park, as opposed to paying the higher costs of flights and stays at the WDW or DL, a certain percentage of them are certainly going to take the savings and make that choice. The alterative is that the park doesn't have the offerings that either of the coast parks do, so for Disney fans, why are you going to make Texas your destination, for a single park that doesn't have the offerings of either coasts.
So really what you're saying is that you're looking to build a brand-new park that is going to cater to the local Texas market, at a price that is cheap enough to compete for local dollars, but not big/enough offerings that it takes away from the coastal parks....at a price point that is going to be profitable? I just don't see that niche market being enough or Disney wanting to get into that market.