Are you aware of the various local authority bodies who have a financial stake in Manchester Airport? Do you not feel that Manchester Airport has anything to do with car parking provision for a vast number of travellers to the airport, some of whom use the access road connections to and from the M56 and the recently new A555 road connection.
I am aware that Manchester Airport Group is a nice little earner for the coalition of local authorities which run it. This is presumably the main teason why they are obsessed with promoting its use and infrastructure links to it. It doesn't suggest that they are likely to take an objective approach to something they derive financial benefit from.
If you're worried about traffic on the roads surrounding the airport, I'd suggest that you start arguing for improved local transport links. Why are there better train services from Ringway to towns east of the Pennines than to many parts of Greater Manchester ?