Heathrow is not a straightforward peice of private enterprise anymore than Hinckley Point is. There are obvious grey areas where HMG needs to support a business which is fudamental to national infrastructure and arguably should not have been sold off entirely in the way it was.
Gatwick are screaming "unfair" because the venture capitalists who bought it for a very good price need LHR to be constrained to flog it off for a much higher one so those at GIP can add to their yacht collection. By all means allow LGW to expand but not at the cost of the airport that airlines and customers would prefer and the one which supports the economy wayyyy more.
LGW does not have "50 long haul routes" without counting all those once a week TCX and TOM beach destinations. For purposes of business long haul they have :
HKG CX A359 not daily vs 5 B777s daily LHR
JFK BA B772 loss leader vs DY
DXB A388 high Y capacity with no F on many services
The rest is p2p leisure with almost no capacity for inbound investment.
The one recent change is DY and two based B787s but that's little acorns at the mo but is beginning to drive inbound US pax. No other major long hauler even uses LGW.
In the last decade, LGW has LOST : AA, DL, US, NW, CO, KE, CA, EY and QR !! No other airport comes close to losing so many major world airlines!