I do believe that one can generate cross fleet synergies, but not if you use the revenue to increase crewing levels on the long haul fleet, as you suggest.
Anyway, far more relevant is the view that the BA leadership holds on how shorthaul fits into the overall view of things.
IMHO it seems to be viewed as a necessary evil to fill longhaul flights.
When was the last major innovation in the CE product? (Apart from running a flying disco?)