To be honest it's not down to Pembrey whether to accept English visitors or not. They are free to apply their own rules as they see fit but in essence it's the English visitors who are at fault for landing further than five miles inside the Welsh border with the current guidance saying not to travel any further than that. The flight through Welsh airspace is perfectly legal but once touched down they are doing the same as driving to a Welsh attraction which is an act that's currently attracting fines from the Police. If they have a reasonable excuse for the flight of course that's something else but for pure leisure they're in the same boat as the beach and mountain enthusiasts who just risk bringing more infection inbound.
Still, hopefully 'Mr Charisma of Cardiff' will sweep all that silliness away next week and we can see all the Welsh fields back to normal ASAP.