Kobe and Melo NEVER get the perimeter shots that defenders flat out gift wrap and hand to LeBron because it's not an efficient way to defend them where it's the MOST efficient way to defend LeBron. You can argue catch and shoots all you want, how many of LeBron's 3's are shots where he's standing still with the ball and the defender is giving him 2-4 feet to shoot so they don't get blown by and posterized? Defenders don't apply the same pressure on the perimeter to LeBron as they do Melo and Kobe.
"Also, Carmelo was assisted on 90% of his threes in Denver and 77% in NY compared to LeBron's 61% last year."
True, but he was a much better shooter in New York (42% vs 33%) when his percent assisted dropped. Took less "open" catch and shoots in New York but shot a better percentage. Give Carmelo the ball for the whole game like LeBron and I'm sure he could shoot 5% worse from 3 with a smaller percentage of them being assisted.