O'Brien is already the Hero of Setlik III. He's the living embodiment of a romanticized view of a military campaign. Setlik III was an invasion by Cardassians. The canonical holoprograms that O'Brien and Bashir engaged in were the Alamo, Battle of Britain, Clontarf, and Thermopylae, all one-sided invasions or attempted invasions by an opposing force. Ezri saw these as annihilation fantasies, although that doesn't strictly fit Britain or Clontarf, and it seems that O'Brien was the driving force behind these, with Bashir just wanting to be a dashing hero in general (see his unrelated James Bond programs). O'Brien wants to relive Setlik III, maybe work through some issues, but he doesn't want to do it directly or openly. He has also strived for historical accuracy, so the Alamo is probably not John Wayne's version or even Billy Bob Thornton's. The Mexicans won the Alamo, but the Texians won the war. The Persians won Thermopylae, but the Greeks ultimately fought them back. Clontarf was barely won by the Irish, with High King Brian Boru (who O'Brien was set to play) dying in the process. Britain was arguably very close to losing to the Nazis in the Blitz. The Cardassians seemed to have met their military objective at Setlik III, even if fought back by the Feds later on, but they ultimately lost their overall objective in the Federation-Cardassian Wars.