heidelberg,
I suggest that as with many routes where FR compete, frequency really isn't prime concern. Just being there will pull enough pax their way, and lower frequency means they can get higher yields - especially as the 738s have more seats to fill than rivals' Airbuses.
Ironic if BLL does turn into a base as we are discussing the BHX car park, as BLL is one of many axed routes from BHX.