Yeah, saying "one shot" in replace of "first try" is stupid. In any game, one shot has always meant killing in one hit, or in some cases, an enemy being one shot away from death (ex: Halo or COD)
I bet you that most people who have played MMOs will disagree with you. Saying "one shot" to describe killing something in one attempt has been an extremely common term for like 20 years. Before Halo and CoD even existed.