When I was a business flyer to LHR and LGW (change at Norwich) the loads were always high with a large majority going longhaul.
I think LGW is set up better to serve the local business community, i.e. oil, petro chemical, good european and shipping destinations etc. An easier transit airport than LHR.
LCY would fail in my opinion because of no advantage in connections and the fact that a visitor to London can drive to Doncaster or Newark and catch a train every 30 minutes or so to London and return by turning up at the station and catching the next train within 30 minutes. A big plus if your meeting finishes early, say 1400 and not 1700. the train is available but you would still be on the evening flight home, if you had flown down on a day return..