You don't have to assume that, or anything else. Livingston played a lot of his limited career as a combo guard, playing SG next to players like Sam Cassel with the Clippers. There probably isn't a perfect comparison for Carter-Williams, but if I had to come up with one, the closest would be Livingston. MCW might be a better passer and might be more durable. It's just sometimes hard to judge a player like MCW and project how he'll do in the pros. So I look for players with similar physical attributes, similar quickness and skills, and try to predict whether their games will translate to the NBA.
I would probably give the edge to MCW over Trey Burke for the Jazz, just based on size and length alone, as well as the ability to finish inside. Trey Burke's biggest knock is that he's really under 6'0", so it limits his upside. Some teams might think he's not really a starter if physically he compares to players like Jameer Nelson and J.J. Barea. Chris Paul might not really be 6'0", but he's a world-class talent surrounded by good players to pass to. FWIW, I like Burke as a prospect more than Kemba Walker and Jimmer Fredette, because he's a real PG with good skills and toughness.
I'd rank the PGs as MCW, then Burke, then CJ McCollum right now.