The issue is that first person mode also give you less peripheral vision. Even when auto sprinting and using the eye icon to look in different directions, you can turn 90 degrees in either angle, while in third person mode you can turn the camera around 360. This, in addition to the narrower field of vision you'll have when moving between obstacles and through buildings, can change how the game is played for you. You'll have to turn and check your horizons and corners more often. Keep it in mind though, and use it against your opponents.