That leaves out the necessary component of getting what you want by compromising relationships, which is the critical component of being a gunner. A gunner is not just someone who works hard and does well. Meaning you can be gunning for a promotion, but if you are a gunner, you will sabotage others to get that promotion, not just get it on your own merits.
As I mentioned on another thread, it's that old joke about two campers who come across a grizzly bear. A gunner is the one who knows he doesn't have to be able to outrun the bear, just the other camper. So he does what he can to trip him up. This is not a label you want. You see some degree of this in medical (and law) school. Other classmates who are more obsessed with how others are doing than learning the material. In the early years it tends to be people who try to psych others out, or who disseminate useless info in the hopes of wasting people's time, or in PBL presentations read ahead on other people's topics to stump them. In the clinical years it sometimes manifests itself into folks making others look bad in front of attendings, or volunteering others for unsavory tasks.