This line of thinking is beginning to annoy me (not by you specifically by the way...)
Martinez got 3 years because the wheels fell off half way through season two. If he was the same at the beginning than he was at the end then he would have been getting questions asked too. Similarly if Koeman started off how Martinez did then he would be getting less questions asked of him.
Of course he needs time, but 3 years seems to be an accepted amount these days. If he is crap he is crap, you dont need 3 years to prove that.
I'm not saying he is crap by the way either....