I will be the first to say that I don't think Simmons needs to be a perimeter shooter to be a good player, but what proof do you have (besides it's early in the season) to say that he'll be a good 3P shooter? It's not 4 games... he's 164 games into his career. He has taken 17 3P shots. He's also never shot more than .600 from the FT line. Besides optimism, what do we really expect to be an improvement? One attempt per game at 30% would be a start. He is nowhere near that and that is still pitiful.
He's a good player now. He could be a great player with an outside shot. Aside from some offseason videos in the gym, there is nothing to suggest he'll be a great shooter. He didn't shoot in college.
He has all the talent in the world and probably could be a good outside shooter, but there is simply nothing to suggest that he is or will be.