I'm a former valley kid that teaches elsewhere now, and if I wanted to put my finger on the biggest differences, it's that Valley schools don't see high level competition week to week. Think about this: you're in Leander. You play those teams, you see their shows, you get ideas from them, and they get ideas from you. It's very symbiotic.
There's a reason why 3 ISDs had 2/3 of the finalists - Lewisville, Leander, and NEISD.
So the isolation is a big factor, more than a lot of other things. Valley bands are good - and they sound amazing a lot of times. It's a different world, and being so far away hurts a lot of times.