Good post. I'd add that Malone wasn't even *that* agile, at least nothing like LeBron. The Mailman was a great post scorer, a fantastic passer, had a fantastic midrange game and just knew the pick-and-roll better than maybe any non-PG ever. His huge frame and solid base let him set picks that nobody could match. But his game was based on strength and intelligence, not really agility.
LeBron is much more similar to Shaq. If you put his skill set into a traditional NBA body (for Shaq it would be 6'10, 250, for LeBron it'd be 6'5, 210) he'd still be a very good NBA player, maybe an All Star. But it's the fact that you have this guy with these prototypical talents in this incredibly non-typical powerhouse, oversized, athletic body, without giving up much in the way of speed. Sure, Shaq was huge, but in his prime he moved like a guy who was 6'10. LeBron is similarly massive for his skillset, but he moves like a guy who is 6'5. When LeBron goes to dunk, you pretty much have to treat him like Shaq or it's going to be an and1.
LeBron, of course, has a much better motor than Shaq ever did. Which is why he's added the three point shooting and defense, and why I think he'll have a more impactful career. And he's smarter and a better teammate.
But you think of the other greats in the game, and there are precious few examples of guys who gained such a massive advantage through a combination of strength and size while maintaining speed and agility.