What makes you think the top clubs would all be in ECNL if GA didn’t exist?
We ran that experiment. Without a second league, ECNL restricts membership in an effort to gain a competitive advantage in local markets. You end up with top clubs outside ECNL because the other top club in their area doesn’t want them in.
If USYSA had half a brain, they would have constructed a system with multiple levels above the local club scene. The ODP state/regional/national structure was their best effort, but that was all part-time with most players spending more time with their club coaches, more or less guaranteeing inconsistent training. Development Academy was a half-hearted attempt with the weakness (other than the obvious lack of funding) was to leave the local clubs in charge. ECNL is just another gap-filler.