The title is pretty self-explainatory, but i prefer giving more information and some proofs.
I started noticing this in the fight pit, where I like using the Spider (with 1500 tenacity). It shooked me the amount of time she remains stunned even though the big amount of tenacity when she's hit by cyclops stun.
So I tested this on chapter 21, "In the arms of a Tomb Angel" (it has a crab, the minion I needed), with two combinations, both involving Plant Soul (I selected her because of her massive tenacity and durability).
First combination: Cyclops and Plant.
Relevant stats from heroes:
-Longer disables: 0% (I took his runes off)
-Stun duration as stated in the ability: 5 seconds.
Video (the second time there's a timer):
Second combination: Moon Drake, Medusa and Plant.
-Longer disables: 61.32%
-Stun duration as stated in the ability: 7 seconds. (Since now there's some longer disables, it should be more).
Moon Drake: not relevant.