Is Expertise stat working?

I play Scrapper. My test is as follow:

I go to training grounds. I give her 1800 Expertise and I set Crushing Smite with Amplified Damage mod.

It applies the debuff to the target which increases its damage taken by 6% for 8s.

With 1800 expertise I would expect the debuff to last around 78% longer but it isn’t.

It is dead 8s both on scarecrow and any other named mob I spawn.

I went and tested in a world with a named mobs and it is the same the duration doesn’t seem to increase.

Whats going on? Am I missing something?

Yes it’s working. I thought the game is broken or something. Basically “debuff” only means hard CC. Stunt, free…etc. I tested it.