Nightblades aren't about "finding" people they're more about just killing people.
In my view nightblades are all about the offense and I think see invis is more to not be ambushed than it is for killing people.
But to be able to see a person is a great thing when you are trying to kill him/her. And how are anyone able to kill anyone else of they cant find the target, thats why we have transgate and other spells.
Besides, unless a nightblade is killing another nightblade the invis would (or should anyways) end on the target making it a non-issue.
There are some skills NB's posses that u cant use against invis ppl.
