Its fine imo.
You have to time the skill correctly, or else you might die from an auto attack after the duration finishes. (Well... in savage fights... maybe even large trash pulls in dungeons too) Also the healers have to heal you back up + like you said, you can't even move. While the other tank invincibility skills like living dead and hallowed ground are much easier to time and use. I main pug savage, so I'm sure holmgang is godlike when you have a static.