It does seem a little odd, although I would not write it off entirely as it was only mentioned to be 'a plan' in the sense that it is one of many options. I could perhaps see some of the lower yielding and more O&D based 3 class routes (BKK springs to mind) move to LGW to make room for longhaul expansion at LHR but I do agree moving all 3 class 772's does not make all that much sense