Good post Teeth! You have learned well.
I've written page up and page down on this, but the best argument is that it is more challenging and more fun. You have to love dying to teammates, to arrows, to get 1shotted by cav. For strict Ninjas you curse the close to nothing head armor. But you have to love it. These are the rules you live and die by. There is no more tweaking of armour, weapon or build combos. Just you and your katana.
It's a little game you play with yourself. Last gen before I took up throwing again, I always spawned with a bamboo in addition to kata, and made a rule for myself to never leave my bamboo behind. If I dropped it, I always picked it up and I got loads of kills with it, and some fubar situations because I didn't drop it. A modern classic is to drop it on the ground and pick it up just as a lancer thinks you are an easy victim.
If flanking, always bring heavy throwing or bamboo. Do the unexpected, use terrain to not get seen, hate the archers and kill them, facehug the shielders, trick the 2handers, kite half the enemy team and split them. Everything is possible with a Ninja build, it all just comes down to your skill, and you are constantly reminded of how much you suck.
It's not recommended for nubs though, or KD ratio minmaxers. It is a great way to learn, think and get better though.
The mind is the armor.
(Without being clever you will get nowhere as a ninja. You are not going to be the mass battle hero. (Except Khorin who sometimes get's out of extremely hairy situations alive.. Create the situations you want to have, avoid the ones you won't win.)
good luck!
PS: Another enjoyable thing is the reactions from other players. Some get's scared like hell, omg ninjas style, some rage seriously, while others (good minmaxers) just laugh. That's why it's so satisfying to kill them from time to time.
(I'd also recommend an 18/21 if u dont have a mw katana. If you do, go 15/24 or troll around with 12/27, but don't expect to be very effective with the 12str one, although u will have fun. )
PS: Did I mention that you have to always block first? Even half the shielders outrange you.
PS2: oh.. And every kill you get as a Ninja is immensely satisfying.. Try it out.