That requires experience for the players and GM. Which is not really a newbie friendly approach to learn by killing characters.The players would then know because they (or an ally) were hit one or more times & can make some estimations based on that along with how the GM describes the attack.
Nor really a good role playing either to use players knowledge.
I was a rogue. Still wouldn't want to be one-shot as a wizard either.Squishy characters like a wizard were by extension squishy
Again. I am aiming for losing the mission, not the character.