i would bet that there are currently lots of people who would beat LeBron in theoretical basketball, but don't have the body nor the endurance to compete.
But with a mecha-suit, the advantages of any natural born talent, and any issue with endurance or strength, etc, are diminished, leaving only mental capability as a differentiator.
That's not to say that LeBron's mental capability (in regards to basketball) is low - surely it's high. But the combination of high athletisism and mental capability is a rarity right now. Removing one of these conditions (via the mecha-suit) will then increase the pool of "high" performers imho.