Although from a passenger point of view it would be more useful to get a service from the North Downs to London than to Gatwick, but it appears the few passengers using Gatwick get more priority than the thousands of local commuters as ever. Powerful lobby group is Gatwick
Hmm, I'd say that I disagree with that. For the major traffic centres between Guildford and Redhill (Guildford, Dorking and Reigate) all already have services to London. Guildford's are definitely quicker and will be better, so it is only any traffic to Croydon that might use them. Dorking I don't know about timings, but I would guess it will be a similar scenario. And Reigate already has the London service, and unless a London service from Guildford was in addition to that, would see no change.
This leaves the minor stations, most of which don't even justify a service every hour (I know this is largely due to pathing issues) And most of them are rural, and so people would likely drive to them, and so could just drive to another of the many fairly local stations with much better services.
Another Gatwick service on the other hand has significant benefits to much of western England and wales who do very much use the line to get there. This is in addition to the not inconsequential traffic originating one the North downs wanting to go to Gatwick; either because it is a major employment and leisure destination, but also to change for better connections to much of southern England.