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.
It's a super rare archetype of athleticism/size+mental that only the likes of LeBron, Jokic and Magic Johnson have occupied (not meant to be an exhaustive list).
I think a huge part of most sports (especially combat ones) is muscle memory. You don't have time to think between moves. So if you want to be good you'll still have to work for days and make your body learn.
And if you think muscle memory is bullshit, try to remember how driving was hard at first and nowadays you can almost sleep through your commute.
Another analogy:
"A good archer is going to be an amazing sharpshooter and therefore I only want to field archers (with guns) as soldiers", might be a horrible way to run a modern military.
This "the best at the old thing will be the best at the new thing too!" needs to die in a fire.