Holiday makers, whilst spending a little in the UK on their holiday, spend most of it abroad
This isn't the issue here. Holidaymakers travel by air and will continue to do so, probably in increasing numbers. The SE airport system must accommodate them. LGW is ideal for this role.
None of the airlines you mention carry export goods.
So are you suggesting that EasyJet, Ryanair and the like don't require runway slots in the course of their daily operations? That is the point here, not the UK balance of payments.
And no, SLF don't count.
Afraid they do! Take a good look at the holding point at LGW. Their flights
must be accommodated within the system.