You are correct to question the ability of BAW to operate from both LGW & LHR to JER. I feel that a doable frequency would be 3/4 services from each. LGW does offer more connections now - but nowhere near as many as from LHR .Certainly as far as BAW are concerned. Another suggestion would be for BAW to concentrate on LHR-JER with 5/6 flights per day, & leave the LGW-JER service to EZY. It would then be possible to connect with all the flights we could possibly want to connect with from both airports.
None of this is likely to happen until the 3rd. runway at LHR.