Um, what about that time on the Enterprise when he got possessed by some ancient evil and held his family at gunpoint and was this close to killing them?

Or that time he had to deal with his former captain trying to start a war with the Cardassian.

Heck, O’Brien had already survived Setlik III long before he was in the transporter room.

Truth is, O’Brien’s life in Starfleet is just one long line of suffering broken by periods of occasional peace.