You should remove Freddie Roach, he's more than proven his merit as a trainer. I agree about Hunter, he's really, truly not a good trainer at all. Alton Merkeson is the epitome of a one hit trainer, he just so happened to be in the corner of likely the most physically gifted boxer in history in Roy Jones.
Let me throw a curveball into the eqaution. Are Enzo Calzaghe and Angel Garcia 'one hit wonders' because they only led thier sons to stardom?
I don't think you could class either of them as great trainers. I would actually say in the cases of Father-Son pairings, merit can be given IF the son ends up very technically sound. As clearly bad as Mayweather Sr. is for ANYONE, he, coupled with Rog, may have a case at being great trainers as they taught Floyd to be a pure technician. Joe Calzaghe is not a technician.