Another point about PIK and GLA is the lack of city routes available, if I was management at Prestwick, I'd be pulling out all the stops to beat Glasgow to the punch and attract a regional operator (with CRJ's or E-jets) to operate routes to major German cities (Hamburg, Berlin, Frankfurt, Munich), the major Scandanavian cities, Paris, Amsterdam and Brussels because there is a market there for business and leisure routes there.
These are relatively "high cost" aircraft though and Ayrshire and the West of Scotland are pretty price sensitive. It was no accident that Ryanair moved the bulk of their city destinations out of PIK when EDI became a base. PIK was already linked to Paris, Frankfurt and Brussels with FR until this happened.
Glasgow can't even connect to Paris or Frankfurt with their respective flag carriers and own connecting hubs which gives an indication of how strong that market really is.
Last one to try was Transavia out of PIK and that died away once everyone who had ever wanted to try Amsterdam had done so.