I think you can turn it off in most games that feature that but it's often still pretty essential, because it's alll build around shooting health bars down and different weapons take more or less health, so it's better to see how much damage you do. That's not really necessary anymore the moment they do as you say - there is a head, you put a bullet in it, it's done. No need for numbers, not even health bars, because the priority tends more in the direction of authencity. We often don't have this stuff in shooters because we know an enemy takes X hits and it's less about the used weapon but what body part you hit and if the enemy has some kind of protection.Numbers flying off bodies are not a real concern, by the way.
They already confirmed you'll be able to turn them off.
Still, are the core mechanics underlying the system that concern me. If I shoot someone in the head, I expect one or two bullets to be enough unless he has an helmet or some sort of cybernetic reinforcement.
I absolutely do not want to see a naked street thug surviving five headshots in a row (or worse) only because he's level 20 and my gun is level 5.
What you describe is my main concern too, I simply don't want to engage in a mission and fill everything, heads, legs, arms, chest with bullets, just because "level 20 thug with 2.000 life points hit by level 5 gun that takes away 5 life points per bullet". I hit a leg, the enemy should slow down. I hit an arm, maybe that enemy loses the weapon, I hit the head - it's dead. In any case something does take more hits, I rather want to actually see the development of the fight, like protection breaking apart and falling off.