yes this may well be the case. As AB seem to mostly fly Q400s from Germany to STN perhaps they'll shift to LCY and the OW set up there, which is where a lot of those flights started off years ago when Eurowings (I think - or maybe some predecessor) flew those routes.
I suppose LGW is also an option for some connectivity but I would think that slot issues would preclude any wholesale shift to LHR.