Harm is that mages have ZERO chances to win a fight against a warrior pre-20/25, unless they are geared and prepped to kill a warrior with some evil wand. So it's perfectly fine that they may at least use invis to save their lives, because on low levels it's definitely not a fair fight.

And from what I know, you become an applicant and get truesight on 25th level. Unless it was changed.