They are armed in a standard LEO type of way. Occasionally, there may be a few who are armed heavier.
Yes, Heavily armed LEO inside the airport would be a great deterrent. I think the heavies mainly hang outside in the shadows waiting to spring into action.
25 years ago the Zurich airport was heavily armed and using sniffer dogs.
The US started using the dogs to catch the meat smugglers due to mad cow disease. Now, you see the dogs for bomb sniffing on a regular basis at some airports.