Well, the other reason you see a lot of long ball played by AYSO teams is because they are very heavily influenced by the English system. Whether the UK International camp, consultants that are hired to develop the material, trainers that come in to help the parents coach, or the way higher level AYSO officials were taught, you see a lot of connections to the UK. And from just seeing my son's little YouTube English penpal play (have posted some of the videos before), at the younger youth levels the English seem to be worse bootballers than us.
The problem often overlooked with Mexican leagues is that they also have daddy coaches, and those daddy coaches teach in the style they know...the Mexican style. It's very physical and doesn't really emphasize pretty technique like skill moves or passing lanes. That's part of the problem when asking what is "technically sound"....we don't have established parameters for what the kids should be learning and how they should be playing and that isn't being communicated to the parents. One of my rec ARs this weekend wanted to get into a long debate with me over why the buildout line is stupid....didn't get it all and the guy knew soccer (huge Premier League fan and with a daughter who played in higher level club).