Why is NIN considered OP or highly viable?

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?

Trick attack is essentially an AoE buff like Embolden, Battle Litany, and Brotherhood. In fact, it's better than all three. You could argue it's better than Litany and Brotherhood combined, especially because of it's incredibly low cooldown. In high levels of play threat manipulation and management is actually super important, a NIN being in the party during Heavensward basically guaranteed that tanks hardly had to generate any hate or make any effort to. As it stands right now, NIN also does incredibly well with personal DPS and while it is getting nerfed it probably won't negatively influence it too much.

Although yes, Trick Attack is the main reason.

Trick attack +10% to 7-8 players every 60sec.

So its all based around that one sole debuff?

yes. Also nin dps tie with mnk.

It can use ninjutsus, ninjutsus are cool

NIN managing agro for a tank means tank can dps harder in dps stance resulting in more dps.

Having the slashing debuff isnt what NIN is used for. (Though it can be)
If a WAR or SAM is using it, that means a NIN can gain the benefit from them using it too.
And you know every group has at least 2 slashing PT members (the tanks) so you're adding a 3rd, regardless who is using the slashign debuff. (4 in the case of SAM, the more, the better!)

And as said right above me, giving more threat to the tanks also means more DPS combos, and in the case of DRK, it can also mean more survival too. (TBN taking up MP, which is tied only to their DPS combo)
Only slightly for WAR as path heal is a nice bonus, but not that strong.
PLD wants their DPS combo for MP as well, for their nukes, but doesnt affect their survival. (that im aware of yet.)

Then while most bosses have enrages, the real trick is usually the smaller DPS checks that happen in the fight, which require timing your burst damage around, which is where things like trick attack shine.

They lost goad (sorta), so thats no longer a thing in their favor.

Obviously a BRD can do a lot more support, but a NIN was the best melee support u could have before, and still decent now.

Also trick attack cd is incredibly convenient since as long as you just use it on cd, you will manage to alligne it with most group buffs.

You really have to understand how powerful trick attack is. It's 10% dmg up for EVERYONE. For 10s, every 60, seconds.
Compare this to Brotherhood, 5%, doesn't effect you, only effects physical attacks, and recast of 90s

And Battle Litany, crit up on a very long CD.

It just doesn't compare, at all.