I have allowed players to describe some kill shots for decades. My rule of thumb is the kill has to be an important or particularly tough opponent, and the final blow either comes after a LONG tough battle, or a crit/massive damage roll. Even then it's usually only 1 time per player and not every session.
Further, if a player doesnt show as much interest in describing the kill shot, I dont ask them to do it, or ask far less often. sometimes those players will decline an offer, and I narrate, on occasion a player asks to describe the action on a dramatic kill, so I allow it.
My players seem to enjoy the way we do it, so that's good enough for me.