Yes.
1. Airports built far out from the city they serve have a universal approach of being panned by their customers. Look at the waste of money at Montreal Mirabel (now closed) for a classic example. Fortunately for Air Canada they had Toronto which became their centre of operations to fall back on. It played a significant part in Montreal's loss of being the commercial centre of Canada in the 1970s-80s.
2. Passengers do not just go to/from the city centre. Look at Heathrow, only a minority do. What proportion of those going to Heathrow use the Heathrow Express from Paddington ? 5-10% ? Why else does the M4 spur out of Heathrow have 2 lanes turning west along the main M4 and only one lane towards London ?
3. Many passengers, most notably those in premium classes, have located their homes and to quite some extent their workplaces (where they can influence such things) to be close to the transport links at Heathrow. Only a limited number of business sectors (Finance, some media) now locate their offices in Central London.
4. Airports far out are commercially impractical for domestic operations, and these services depend on 50% connecting to overseas flights and 50% local domestic passengers (including many day returners). Split this market and you can lose the whole lot.
5. There would be just as much opposition to the proposal, particularly to its surface links, new town developments, etc, as there is to the current locations.
6. As a recent failed operator based at Manston will tell you, the lower Thames estuary/seawards has very little hinterland demand for air travel. 75% of the catchment area is water.