then the US pushes a lot more aircraft through its busy airspace this way This may be true overall, but San Diego is barely top-25 in the US in passenger traff

then the US pushes a lot more aircraft through its busy airspace this way This may be true overall, but San Diego is barely top-25 in the US in passenger traffic. And Heathrow is busier (even measuring per runway, since it has 2). And both Gatwick and Mumbai handle more flights on a single runway.