Right now, for the playoffs, James is 16-30 on threes, and that's with a man on him.
Giving Lebron a 3ptr is just about the best situation to have him in. Lol you would rather have him driving to the rim?
I agree, with a caveat. They cannot be "comfortable" 3 pointers in the flow. In other words, you cannot let him really step into them.
Lebron has become a decent to good shooter, but he is more like Pierce than Ray Allen. He needs to step into his threes, and does not have a quick release. Allen on the other hand (and other great shooters), have such a compact motion, they can shoot in rhythm with incredibly little space, and it doesn't affect their form, or have a huge affect on the chances of the ball going in. Shooters like Lebron, who are not as "pure", can be thrown off if you get up into their body, or throw off their rhythm BEFORE they shoot (meaning, running them off the shot, after they are in motion does not mean much). This means sitting 6 feet off of him, daring to shoot does not do much, however, if you play off to the side of him (with a help defender taking away the other side), giving him the illusion that he has space, but so he still has you in his peripheral, you will throw him off.
This is what Ray Allen did so good against Kobe in the finals in '08, and what the C's in general did against Lebron early in the series in '08. It seemed like they were just missing shots they would normally make, but what was really happening was the C's were throwing off their rhythm, while still daring them to shoot.