I think this misses the point. Before LPL expanded, the likelihood is that all of those flights would have been from MAN. Therefore MAN has occured a loss of passengers to LPL. LPL may have a lack of connections, but MAN is hardly brilliant in that aspect either.
As for London routes, the domestic (particularly LHR) flights have been decreasing anyway since the west coast mainline work ended and journey times decreased, and to be honest, as someone who has gone down this method, I just cannot be bothered with the security and queues for a poxy flight to LHR. In the time I have queued, waited, been delayed as usual etc, I'm already at Euston on the train. The LHR flights from MAN are still busy is due to the amount of connections made at LHR because the flights don't exist from MAN direct or cost too much and are cheaper via LHR.
LPL may be a one terminal low-cost only one trick pony at the moment, but, the fact that pax who were frequent MAN users are driving further to LPL instead of using MAN shows there is something missing from the offerings at MAN. That is what needs addressing, be nice if that had been done instead of
off the pax even more with T1 arrivals parking charges and horrendous security queues, even at T2 which is hardly a terminal building built before the days of high pax numbers or heavy aviation security.
If MAN wants to regain the momentum, it needs the low cost flights and perceived (or real) convenience LPL is offering, and the routes pax are connecting to via LHR. Until then it's a just a second tier provincial airport (albeit a better than average one)