If he's prepared to be a squad player and Martinez is prepared to use him like that, then I'm happy for him to stay. He's a top lad and has some very good qualities.
But he is not good enough or suitable enough for what we need. He isn't creative enough to play the role asked. Late on in games though, he can be a nuisance to other teams, and one on one with the keeper there are few better players in the squad.
It's okay to have squad players. Not everyone has to be ace or gash, there is something in between. It just depends on whether or not Naismith is okay not playing every game for 90 minutes.