So to give LGW the ability to compete must be better for society in the long run.
Its a mistake to put all your transport nodes in one area as was witnessed recently when the LHR central area tunnels closed for a short period, causing absolute chaos.
Gatwick has competed for years with LHR, what you're asking is for one business where more airlines want to use (LHR) to be held back to allow a second business that many airlines shun (LGW) to compete more effectively. Except the key point is that the routes we need are choosing to use AMS, FRA et al rather than LGW, which is available today. I reiterate recent history.
AA/DL/US/CO/NW all left LGW for LHR of their own free will, with CO/DL/NW/US having said they'd happily serve both. In the end, they walked away from LGW as it was less competitive. The same goes for recent history with CA/KE/GA/VN. No long haul foreign airline will shoose LGW over LHR if they can avoid it with the exception of the likes of loco long haul of Norwegian.
LGW can't compete on alevel playing field with LHR because LHR is a world airport and LGW simply isn't in that league. In terms of connectivity they are miles apart.