I don't believe domestic access between LHR and MME is what's driving the agenda here. HAL want more heavies with a lot of throughput through shops and high charges to pay for ROI on new capacity. A few daily Embraers to LPL and MME won't be the ideal. If runway three does go ahead, the same BA that brought back LBA and INV will be on the march to protect yields and market share. Consequently there might be some domestic capacity increases but likely not a step change.
What happened here is flybe asked HAL "Can we fly for almost nothing?" and HAL said "No, stop being silly."