Lets look at The Ring magazine top ten flyweights - 4 Japanese - 2 Latin Americans - 2 Brits - 1 South African - 1 Ukraine - 0 USA.
By your rationale, the two Latinos will have fought, be based, learnt their trade or ply their trade in the USA, right? They've had 48 fights between them, zero in the USA. Neither are based or live there. In fact, between the entire top ten a grand total of two fights have been in the USA.
So my question is - do you understand the meaning of "strength in depth?"