Operating into LHR has become so expensive that you can only begin to make money using a minimum of a 150 seater jet. I am not sure there is enought business traffic into Heathrow to justify 2 airlines running 319 sized aircraft twice or three times daily from ABZ.
The Embraers were more or less being used by Mainline to protect the slots, and if the flights made a bit of money then it was a bonus.