LGW badly needs more longhaul!
Why? Gatwick is back to what it does best. Charter and holiday flights. It does have a lot of charter long haul and still the BA and VS beach fleets. What people long for is the return of the legacy carriers from LHR. There seems little reason for that to happen and new entrants to the market only use LGW until LHR opens up a slot they're able to bid for.
No airport "needs" long haul, it's mainly the Kudos that people love, like BRS and Continental, major bragging rights. I doubt it makes much difference to the bottom line.