Howdy Flyer,
BA no longer operate to Montego Bay, just Kingston which is 4 times a week and always full. Primarily full of UK expats and those returning to visit families from Jamaica, usually in and around the Kingston area. I reckon the VS flights will be primarily holiday makers unlike the ba flights! So i doubt there would be very much competition. Especially considering that the KIN route is basically a PSO route for the commonwealth from the old BOAC days!