Honestly the NBA is changing, and while I agree with you when I have my old basketball hat on, the new NBA has spots for a Grant type player. Especially if he can be solid from three. I think his mid range game and free throw percentage show he can definitely develop that. Not comparing their games, but Draymond Green is a perfect example of how successful undersized 4’s can be in this era.
Draymond is a defensive freak because of his massive wing span. He's the same height as Grant with a 7'1.5" inch wing span. 4 or 5 inches bigger than Grant's. Draymond rebounds and passes and plays defense. Not sure he's a good comparison to Grant other than his height.