Isn't this roughly what it ought to be? The market early is Southbound driven, going home North late. The oddball is the easyJet LGW-EDI / GLA which operate from the LGW end (!)
No - Gatwick domestics always used to do OK on morning departures ex Gatwick. If you look at where a lot of the higher-yield passengers who work in London during the day actually live (and 50-60% of the traffic originates from home, not from the office) then Gatwick historically did reasonably well on this traffic. BA has systematically trashed the schedules by moving morning departures much earlier (to 0610-0625) and evening return flights much later. There is a market and a lot of the morning southbound traffic into Gatwick was connecting onwards rather than point-to-point.