Exactly, Easyjet will always use Luton as an alternate due to availability of staff and handling familiar with aircraft so reduce potential out of hours and staff/transport unavailable at short notice. I think Luton now keeps x3 A320 capable stands for diversions now.
I feel for the BA Euroflyer pax who ended up at Cardiff.
Case in point, x2 Air Indias went to LHR where handling is well established. The Vueling & Air Europa pax if as was stated got dropped at STN and positioned back empty to bases, not so nice if sitting in LGW departures to go to Spain.