In any case isn’t the sole reason there is ‘little’ leisure traffic (bucket & spade) at LHR because there has been no space for it? If the likes of Orlando were served from LHR or airlines like TUI based there I’m in no doubt they would be packed to the rafters.
The reason for that goes back to when BAA owned them both and purposely separated it that way. Business at Heathrow, Leisure at Gatwick and also Low cost from Stansted.
Who remembers the arguments for expansion not long ago and whether Gatwick would be a viable alternative to LHR? I think we are currently seeing exactly how much the airlines and passengers value Haethrow over Gatwick. I expect Gatwick will become pretty much short haul loco only for a long time.