As more player available stuns have been introduced to the game the number of unstunnable mobs has increased proportionally
Stuns were also changed to just resetting and not interrupting casts
Blizzard are in an arms race of their own creation
Is assigning a talent point to get a stun no longer worth it?
Many people don’t seem to understand that NPCs also have stun diminishing returns. Each subsequent stun gets shorter until they become immune. My groups spam then all instantly even without an ability being cast we need to stun. lol
Stuns are still pretty much worth it, but you only get their full power if you coordinate it and mix it together with other effects like disorients and knockbacks.
With the right setup you can still keep a pack locked down for a long time. For uncoordinated groups it still has some use.