How are Crit Chance and Poison / Burn Damage calculated? (Assassin's Creed: Valhalla)

A large number of weapons have a critical hit chance of around 50 by default, but this is obviously not 50%.
Now about the poison. I inserted runes into the weapon giving + 4 damage from poisoning, the enemy received 5 damage each. Removed the runes, enemies still take the same 5 damage from poison.