While PF would have a tough time on the traditional TATL ex MAN (NYC/BOS), there could be a niche to carve in new routes like Washington, and adding capacity on Toronto and possibly PHL.
As far as intense competition goes, it didn’t stop PF adding CDG against AF/D8/XL and so on, and while STN has limited TATL, London-US (when looking at the bigger picture) is hardly devoid of competition, is it?
But saying that, I don’t think BHX should be worried if MAN TATL does happen. PF would be competing with MAN based carriers, not its own services at BHX. The timetable at BHX should be more than capable of standing on its own 2 feet regardless of what happens up the M6.