vastly underrating Bird's athleticism.
One of Bird's issue, which even he mentioned about playing Rodman was the Rodman didn't easily fall for his fakes, and as a result, Bird wasn't quite able to flummox him with a followup fake, shake, & move. He was then in a committed play which is the result of not having the same foot speed of a quicker defender. If LB's brain had a LBJ's body, he could bamboozle Rodman all night with higher speed combinations and thus, draw fouls constantly without end. Rodman would need constant help defense, Bird would then dart the ball off to the driver in the open lane. The Pistons of the late 80s would not have an answer for this beast.
vastly underrating Lebron's "Bball IQ"
Bird's passing requires psychic skills. It's seldom that one would have one's back towards two defenders, not seeing who's where, glance away from the two fellows (with a split second fake move to pivot, thus generating the distraction), and dart a pass over two men w/o either of them seeing it, in time for them to throw an arm up for deflection. Realize, there's four potential arms there.
Sorry, but the present LeBron can't do the above. He's a good passer, but not a truly psychic one. Now, give LBJ's brain Bird's body, and during double teams, the passes will start to get deflected away, leading to a turnover. Thus, he'll limit his passing to that of the standard back cutter, no-look behind the back during a run 'n gun, etc, then anything of substantial psychic prowess. He'd clearly be less of a player.