I am wondering why people do (and have in the past) hold NIN as such a highly useful and needed class in the game?

It seems everyone thinks there needs to be at least 1 nin in serious groups for hard content...why?

I play nin a bit and did a lot of it last xpac but I dont see why its held so highly.

Is it because of the vul debuff from trick attack? When I ask people why they think NIN is so strong they say its because of its high amount of utility for the raid...but trick attack is the only unique utility I see it having compared to others.

It doesnt have an AoE buff like embolden or battle litanyor brotherhood

It has a slashing debuff that is brought by sam and I think warrior still

It has threat manipulation but I would think at high levels of play threat is a non issue...and even in low levels of play I dont find it being a bother enough to use skills on

So is the vul debuff the sole and only reason NIN is held so highly?