Routes to MIA and BOS with AA will have a better prospect of lasting when BA and AA gain anti-trust immunity. As it stands BA couldn't be bothered codesharing MIA lest the premium passengers that it does carry MAN-LHR-MIA decided that MAN-MIA non-stop would be better.
AS for Jet2, look at the September provisional figures released today and you can see why they're not committing to non-bucket and spade routes ex-MAN at the moment (perhaps with the honourable exception of Budapest). Emirates shunted 347 passengers per fllight, Qatar 245 per flight and Etihad 195 per flight. Each had double digit growth over September 2006