I find myself feeing sorry for Nick. He was rejected by most of the designers when choices for mentors were made, which crushed his ego. Poor guy! Thus far, his mentoring style is simply black or white. It seems he wants to help his team so much that he completely takes over OR, as witnessed in this last episode, he washes his hands of them. Nick's heart is clearly in the right place but mentoring doesn't seem to be a skill he possesses. Everybody can't be a Tim Gunn type. He was born to be a mentor. It's in his DNA!
That said, the flaw of the show having the three mentors. IMO, they aren't needed....at all.