The debate about where to build a new runway in the south-east has meandered inconclusively for several decades, so Boris Johnson may be to right to think that a thumbs-down for his Thames estuary super-hub from Sir Howard Davies's Airports Commission is not the end of the story. The decision, ultimately, will be taken by politicians, and political sands can shift.

Yet Davies's latest dispatch ought to sound the death knell for the estuary fantasy. Choose your own clinching argument from the list of objections, but the top two are surely cost (£30bn to £60bn more than competing projects, estimates the report) and the sheer hassle of closing Heathrow.

As the commission says, there are no international precedents for an airport being moved 70 miles across a city. The economic risks are acute. The mayor of London's promise of a 24-minute journey to London Bridge is not going to cut much ice with big international employers who have invested in headquarters and facilities in the Thames valley to the west of London. When the time comes to move, they may decide that Frankfurt looks more appealing than Kent.

As the commission puts it: "The agglomeration clusters that have grown up around Heathrow over many years could not simply be 'dragged and dropped' into a new location – it could take many years for economic activity around the new airport to grow to equivalent levels, if at all." Quite.

As the commission sees things, the best place for a new runway is either Heathrow (two options) or Gatwick. Johnson spies a "gigantic" smokescreen to allow the political class to perform a U-turn on expanding Heathrow. Again, his suspicions are understandable, since the business lobby for Heathrow is formidable and government ministers, or at least some Tory ones, seem constantly to try to backtrack on David Cameron's promise of no third runway at Heathrow –"no ifs, no buts".

But let's not assume (at least not yet) that a giant stitch-up to favour Heathrow is the inevitable outcome. In a world of necessary compromises, Gatwick still looks the least bad option. It would be cheaper, with the planning obstacles less formidable and noise pollution imposed on fewer people.

The argument that the UK must have a single "hub" airport – meaning Heathrow – to make flights to deepest China viable has always seemed wildly overstated. Heathrow struggles to explain why so many short-haul holiday flights, carrying few transit passengers, still crowd its terminals. If we must have a new runway, Gatwick, the only airport capable of providing Heathrow with stiffer competition, looks the best answer.