why is a dagger a d4 and longsword a d8, every one who crits on the eye will do different damage. you firbolt the eye, roll max damage do 20, they crit the eye with a longsword, 2d8+4 roll max damage do 20.
I think the psychology of it is the big deal.
My point is that you hit a dragon's chest with Firebolt, you do 1d10 damage. You hit the dragon's eye, you do 1d10 damage. That makes no sense.
But you hit the dragon's chest with a crossbow bolt and do 1d10 damage and if you hit his eye with a crossbow you do 2d10 damage.
Why is a crossbow bolt more effective on the eye than the Firebolt?
And why can't a monster hit you in the eye at all?
Or let's consider the groin. You hit a hobgoblin in the groin with a longsword and do 2d8 damage (Strength 10). Your mage comes up and hits the hobgoblin in the groin with Shocking Grasp and does 1d8 lightning damage. Um. Something doesn't seem right here. I don't care if you get hit with a longsword or a jolt of painful lightning, if you get hit in the groin, you're going to suffer some pain. Even getting grazed with a jolt of lightning on the groin is enough to drop a man.
The answer to this objection is that there is no "hit them in the eye" or "hit them in the groin" mechanic in Dungeons and Dragons 5e. You are just adding color commentary to the crit mechanic.
You could expand on that if you want to. Maybe when the wizard rolls 20 on 2D10 damage from firebolt you can proclaim that it hit the dragon in the eye.
Also, as an aside, it would be really easy to houserule the crits at your table.
