The height is probably more of a hindrance for Lebron. He would be incredibly easy to hit hard and tackle and he would have minimal yards after the catch.
There's a reason hardly any running backs in the league are over 6-1 (only one I can think of is Jacobs) and few receivers over 6-3 to 6-4.
Nobody outside of the lines is "slow." With Lebron's height he isn't getting any yards after catch, and if you want to compare him to Moss who is in scientific terms "stupid fast" he needs to be very, very fast.
Basketball speed is completely different from football speed. Even in a fast break situation you're only talking about 15-20 yards.