The amount of ignorance (and I want to use a stronger word than that, but I won't even though it is applicable) on this thread is staggering. Some of you need to change your handle to something with "Karen" in it.
1. I am hardly a fan of UIL and think some redistricting decisions boggle the mind. But trying to put it into the hands of the legislature is laughable at best and idiotic at worst. It is political enough; why make it more so. Besides, why make it more adversarial? Legislatures are there to represent their district. They're going to advocate for their area as much as they can. If some of them had their way, they'd put a school like Duncanville or Southlake in a 6-man district and still let them play with 11. At least UIL attempts to be somewhat objective. Sure, they fail sometimes but I don't really think they start out with a "let's put x in y (whatever: district, class, etc.)." The lone exception here seems to be Highland Park, who always seems to be on the 5A side of the split. Either they have a source or UIL really is refilling their water.
2. Football, believe it or not, is not the only sport up for consideration. In different classifications, there are football only districts, football and basketball, etc. Competitiveness rarely factors in to any decisions, nor should it. Aledo can't be in a district with Prosper, Allen, Southlake, Duncanville, and North Shore, but that seems to be what OP is suggesting.
3. If Granbury wasn't in district 3, they'd have to either be in district 2 with Odessa, Midland, and San Angelo schools, OR, they'd have to be in district 4 with Southlake and the Kellers schools. OP, which scenario would you prefer? District 5 and 6 are all Denton and Collin County schools (and Jesuit in 6) while 7 is the Planos, Richardsons, and Coppell. 8 is mid-cities schools. Granbury is where they belong.
4. Any private school can play in UIL. However, they have to play in the class where the largest school in their town plays in. For example, if Prestonwood was going to go UIL, they'd be in 6A because of the Plano schools. Same is true with Parish Epis. If either could go 5A, particularly 5AD2, they probably would. But right now, TAPPS has no problem with either. TAPPS told Dallas and Strake Jesuit years ago that they didn't have a spot for them. Now both are entrenched UIL schools, with DJ competing at a high level in soccer, among other things.
5. I don't know what OP is talking about when he says 6A is a "ridiculous" reclassification. From what I see, it is VERY clean. No Euless Trinity having to travel to San Angelo, for example. Granbury is 50 miles to Arlington Lamar HS. I think that's their furthest trip. Granbury has been over 2200 in enrollment for a while and would have made 6A last year but the cutoff number was higher than it was this year. Overall state enrollment is declining with some larger schools from last time dropping. Granbury got larger, so they move up. Its neither ridiculous nor the least bit controversial. If they're unable to compete, well, that's too bad. Join one of hundreds of clubs.
6. Finally, UIL has a hell of a lot of problems. Just getting into a few, they refuse to get too deep into recruiting, they allow district committees to play politics with rule violations, they let schools skirt rules (both playing rules and administrative) all the time. However, reclassification, while nowhere near perfect, isn't one of their problems. The OP not liking his district isn't proof of anything other than a case of "you need to get over that," and fast.