It is quite possibly one of if not the best tank skills in the entire game. FF14 doesn't revolve around raids, its got hours of other content that TBN shines in just as well
At best you store a dark arts weapon attack, even if you are currently at max timer
Most importantly, its mitigation AND free damage if lag kills you and you just get raised

In raid environments its so strong it allows healers to flat out ignore some damage and keep dpsing even if it fails to break. If it succeeds, you are now dps neutral
In casual environments, you can now start using the moron dps as boosts for your own dark arts when they stand in the aoes


Its the last bit of uniqueness and skill in this Warrior clone anyway >> sounds to me like that streamer is the sort of person who focuses purely on dps and not how fun and unique a job can be