Supposedly he has an ability ("Unyielding Assault"?) that means his Melee Attack can never be debuffed. Zechovich unit tests show him fighting Grimgor with a bug red debuffed Melee Attack around 18:05.  Skulltaker is on his Juggernaut in that video, so I'm betting that the ability will be bugged when he's mounted. Earlier in the video, seems to resist Grimgor's debuff while unmounted.

If only the DLC wasn´t published yet and there would be time to fix things like this...

But hey, we couldn´t feed the narrative of CA being too dumb to crap, right?

You’ll often find bugs but they’re using an older version of the game. I imagine the bug has been reported already.

Nope. The bug exists in the game.

1. Given the rate at which CA patches bugs in the live game, you should expect any bug observed in a pre-release video to be in the released game.

2. Given the number minor bugs we find in these games on release, you should expect that CA has a poor process for bug identification. That is, they probably don't know about these bugs. The game in its basic form has been out for 8 years and yet CA has not figured out how to test their code even for simple things like abilites. CA isn't too dumb to crap, but you wonder if they give a crap about player experience.