There's 0% chance that Murphy could have been an All-Star.
Coach: Jim O'Brien was the best thing to happen to Murphy's career. Best coach possible for him in the entire league. The kind of coach whose system - the spacing, the pace - maximize what a guy like Murphy brings to the table.
Defense: He's one of the worst defenders in the NBA and his "team defense" is as horrible as the rest of it. He's frequently out of position, he's very slow helping, recovering and rotating.
All-Star:
Scoring, volume and efficiency: Murphy is an efficient scorer because he's a good 3pt shooter, but he lacks versatility in his offensive game to put up bigger numbers than those he posted in Indiana. You can only score so much in trailer 3s, spotting up and the very occasional dribble drive from the elbow. Murphy lacks shot-creation skills to put up the type of scoring All-Stars have. The increase on usage rate he'd need would come at the cost of an abrupt decline on efficiency as he'd need to take shots he simply can't make. He's way more valuable as a 15ppg scorer than as a 20ppg one.
Rebounding:He doesn't keep possessions alive in the offensive glass; his value is exclusively as a defensive rebounder. However, his numbers overstate the true value of his contributions as he's basically a glass cleaner who isn't very good getting contested rebounds. He pads his stats with the easy ones that in most cases one of his teammates would get (mind you, every great rebounder, the Loves, the Howards, the Rodmans, the Malones, do this, it's part of the mindset... but they're also dominant on the hard ones. Not Murphy).
Summary: Murphy can be a solid starter in the right system. In a team that can use the shooting from the big man position to space the floor and that has enough defensive quality to make up for his deficiencies (especially a high quality defensive big who can guard both big man positions, defend the pick'n'roll and protect the rim). For most teams though, he should be a 3rd or ideally a 4th big. An All-Star? He just lacks the talent to even sniff that.