The working rights of the the MF CC are the same as they are for the heritage CC.
The rest of what you say has some truth, those that need to connect into LHR are more likely to be affected by the strike than those starting a LH journey from LHR. I think that BA is looking to a longer term game than just the days of the strike. BA must ensure that they run and manage the business rather than one group of employees determining how the business should be run for the benefit of them alone.