Xeviat
Dungeon Mistress, she/her
Can you please define what you mean by "stunned"?
If you mean "target loses an action" that's one level, and if you mean "target loses their action and has defensive penalties" that's another, and "target loses their action via paralyze which makes every hit into a crit" is higher.
I mean the stunned condition:
Stunned (from the PHB)
A stunned creature is incapacitated, can't move, and can speak only falteringly.
The creature automatically fails Strength and Dexterity saving throws.
Attack rolls against the creature have advantage.