There's much more than just mentality between them, although thats probably the biggest difference. Grant might try for a more expansive game, sexier football, blah, blah, blah but he certainly dont achieve that aim. He lacks the tactical know-how to have an impact, his substitutions are borne out of desperation and the need to show he's doing something, not because he's read the game and actually knows what'll work.
As for other differences - Grant obviously lacks charisma, personality, social skills, wit, looks, etc, etc, the list is pretty endless.