To the contrary. It proves quite conclusively that slave money was ending up in New York gentry pockets as well as Washington DC gentry pockets.
You don't want it to prove this, but objective people can reach no other conclusion. Significant amounts of slave money was supporting the economy in New York and Washington DC.
Why else would Seward proclaim that he could guarantee New York's ratification of the Corwin amendment?
It proves that the North consumed imports while the south consumed next to none.