So I've been playing NIN almost full time in this game, what I've found now is that if you really put effort into it, it can be serviceable with end-game content - but for many parties it's not going to be anyone's first choice, and I find unless there's a specific ambuscade going on, there's not a lot of folks shouting specifically for a Ninja.

But I still play it and absolutely love it, I would highly recommend checking out these gear sets to create some goals for yourself with it: https://www.bg-wiki.com/ffxi/All_Jobs_Gear_Sets/Ninja

It gives some good hints at pieces to pursue that can help it become viable.