Again, for the umpteenth time, some people are conflating runway capacity with hub capacity.
1) A HUB is a single large airport with usually one dominant carrier with a large number of intercontinental destinations supported by feed from other domestic and international airports. Think LHR / CDG (less so ORY) / AMS / JFK (no single dominant operator) / EWR / DXB / DOH / AUH / ZRH / FRA / MUC / BRU etc. THis is crucial in driving business support and inward investment.
2) Runway capacity is more concrete to allow people to fly
If there's no intersection between 1 and 2 then your hub is still massively constrained. To be clear, the Scottish Lowland airports are not competing for hub capacity. To be clearer, and this is quite crucial.
GATWICK AIRPORT is not a HUB and has failed every time it has tried and has also lost every legacy long haul airline ever with the exception of the BA/VS Beach Fleet.
If you give LGW a new runway the locos can't pay for and business won't use, what are you actually doing?