BA Longhaul/MAN
At the end of the day US airlines will always have the advantage over UK airlines of flights to the USA from the regions, it is a fact of life.
AA, CO and the rest can operate into their major hubs and secure traffic that is not point to point. This gives them an advantage as UK airlines including BA have no hub outside London to feed any traffic through.
Point to point on leisure routes to Vegas and Florida may be different.
Manchester is well cattered for by other airlines to the states and I am suprised that the BA flight lasted as long as it did.
Centre cities