As to your final point: either the hypothetical founders do not have the support network from YC and simply cannot become the next Big Thing (and someone else a

As to your final point: either the hypothetical founders do not have the support network from YC and simply cannot become the next Big Thing (and someone else at YC/SV does it instead), or they find a different support network - possibly in a different state or country - and the market hums along. It's not a great tragedy either way.