People can come out with all the rhetoric they want about rail links etc, but the fact of the matter is that GLA and EDI are better located and thus more attractive to most pax and there's little any new owner can do about it. The only way over that is to offer virtually zero charges (as FR seem to receive) which brings up the same problem - little income and resulting losses.
From a passenger point of view location is only really considered by outbound passengers - local residents who know the area. A lot of passengers will be inbound passengers who simply don't know which airport is closer to the town, all they know is they want to/need to go to Glasgow, and they have an option of two airports.
Passengers will also be price sensitive - if PIK can offer cheaper flights than GLA, or offer direct services to markets that are not served from GLA, then they can also attract outbound passengers.
Ultimately though it is the airlines that decide where they want to fly. As long as PIK can undercut GLA then they can continue to pick up the occasional low cost airline, probably foreign based that mainly targets inbound visitors to Glasgow. However as we have just seen with Wizzair, it now looks like Glasgow is prepared to up its game and offer better deals to attract low cost airlines, which is bad news for PIK.
That's more than Cardiff .... over 50% more than Bournemouth, or Doncaster Sheffield, or Exeter, or IOM, or Inverness or Southend .... and more than Durham Tees Valley, Norwich, Newquay and Blackpool put together.
Passenger numbers aren't everything though, it all depends on the revenue generated from each of them, and more importantly the fees paid by the airlines operating those flights. We have all read that Ryanair pay next to nothing in fees at PIK, whereas Cardiff is served by KLM and Lufthansa, as well as Aer Lingus, Air Malta, Air Europa, BH Air, Citywing, Eastern, Flybe, Onur Air, Thomas Cook, Thomsons and Vueling, all of whom probably pay higher fees than Ryanair do at PIK.
It is going to be difficult for any new owner to make a profit out of PIK, but not impossible.