So here's the scenario. We have for the first time in my group a Ninja being played (Grippli as well, which is hilarious). He has now reached level 10. He's a Two-Weapon Fighting sort, Weapon Finesse, that path. Now he has the combination of Vanishing Trick, Invisible Blade, and Pressure Points. So with 7 ki points/day he can use Greater Invisibility for 70 rounds/day. Every time he succeeds on a Sneak Attack, he can do either 1 point of Strength or Dexterity damage, so nearly 4/round. He's denying the opponent it's Dexterity for being invisible. His damage output (while wearing Deliquescent Gloves) is 6D6 + 1D4+1 (wielding a pair of Wakizashi) per hit. If he hits 4 times in a round, that's maxing 164 points of damage.
Now yes I know there is See Invisibility, Blindsense/Tremorsense, True Seeing, Faerie Fire, Glitterdust, and Invisibility Purge around to counter this. But honestly I can't find any other class that even comes close to the damage output and defense abilities these few class abilities can grant (and no let's not talk about the Gunslinger :P).
Am I worrying too much? Or do others see this as well?