Is it just me, or does ninja feel like...

[Seraphor]

Agreed. It is a ton of fun.

Maybe something OP is missing is using the ninjitsu within the trick attack window? At least that was what I had been doing and I ended up fairly high on the aggro list at least. Not saying this is the best rotation, but this is what I used while leveling (Caveat, I've only leveled NIN to 80, then moved on to the next class) :

Pre-pull -
Huton (3 mudra ending with Ten)
Suiton (3 mudra ending with Jin)
Hide to reset mudra
Anything to break hide

Pull:

Trick Attack
Shadow Fang
Raiton (2 Mudra ending in Chi)
Kassatsu -> Hyosho Ranryu (2 Mudra ending in Jin with Kassatsu)
Raiton (2 Mudra ending in Chi)
Dream within a Dream
Assassinate
Bhavacakra (If enough Ninki)

At that point just combo until trick attack comes back. Keep Huton up with that combo when needed. You have 1 mudra that you'll use before then. Ideally I use Kaiton, but admittedly, I'll forget to keep Huton up and need to reapply sometimes. Ten Chi Jin should be in there somewhere, but I haven't really figured that out very well. Other than using that 1 mudra, I've just used my normal combos until the next trick attack window.

I'm sure that it's not the ideal combo, but that's _generally_ how I've played it. Make sure you're hitting your positionals too. Normal 1-2-3 combo is rear for the last hit, the Huton reset combo is flank for last hit.

Suiton is a damaging move, so it can't be used prepull. (typically you'd use Doton if the arena and tank pull allows for it, otherwise just stick to Huton)
Instead you would Suiton ON pull, pre-enter the mudra's before pull, but after using Hide.

Also, Ten Chi Jin is one of your more powerful skills, not as good as Hyosho Ranryu, but good enough that you want to get it into every other Trick window, replacing one of the Raitons and likely one of your weaponskills as well. You want the Ten>Chi>Jin combo too as that gets you Fuma, Raiton and Suiton, and lines up with your Meisui for 50 gauge.

Ultimately the Trick window is very malleable, so long as you get your hardest hitting moves in there, you can pretty much do them in any order.