Given his salary, I don't think Rubio is a good option, but unless his shooting is in permanent decline, he would be better than Smart. Not because he is more efficient, but because his playing style fits this team better.
It isn't about the numbers. Smart could be a good fit for the C's, even with his poor efficiency. His problem is that he doesn't adapt his game to fit the team. He doesn't give the team any push in transition, and that is the worst part of his passing game. He tends to pound the rock, and doesn't promote ball movement. He often has poor judgement, and refuses to defer at the end of games to Tatum and Brown.
Smart could push the ball more in transition. He could make decisions with the ball more quickly. He just doesn't.
The overall effect is that he slows the team down, when we have two of the best wings in transition in the league.