Symir is a significant offensive downgrade from Joe or Mintz. He can't create for himself and we just don't have much for him to pass to. Unfortunately, we need guards who can score because our Forwards can't. We could have prime Steve Nash on the court and our Forwards would still suck. His defense is less of a gain over Joe or Mintz than his offense is a loss.
When Girard is ice cold and making stupid turnovers, yeah, play Symir. But other than that, he's just a solid substitute to give the guards breathers.
edit: Per advanced defensive stats, Symir is not an improvement over even Joe on defense. Eyes might tell us something else, but stats say we're better defensively with Joe on the court. This might be an indictment of advanced stats more so than an indictment of Symir, though. For instance, want to guess the best guard we've had by defensive win share? Mr. Shaky Potatoes himself, Trevor Cooney.