I'm pretty sure we all said the same thing when Madrid when from 0x operators to 4x operators, and 3 are still doing well 3 years later!
I think the opposite. AA and UA proved there was a market for this route in 2016 with both flying to NYC. They carried just short of 150,000 pax in a year. Now yes, there will be a proportion of pax transiting through NYC but then these were always higher costing routes, helping to re-enforce a perception of BHX being an expensive airport...
We now have an opportunity to attract a market to BHX in the way that NAX has done at LGW and TCX has done to MAN.