At least for chess the article mentions that they considered the top 10 players in children and senior categories. This would indicate that prodigy chess players are millions of time more likely to become elite compared to the general population.

Exactly. If their metric implies that 1 of the top 10 prodigy chess players became 1 of the top 10 adult chess players, and that holds down the line, then a prodigy has a 1 in 10 chance of becoming a top player, but a muggle has a 1 in 889 million chance.

To be a top child player, you need talent, recognition of that talent, and investment of time and energy.

So, who's to say that the time and involvement didn't make them better as adults than they would have been?

ISTM that if you groom 10 children and even one of them outperforms a billion other potential players, you've done well, even if they had some latent talent to start with.

They claim to "prove" that catering to young talent is counterproductive, but this certainly doesn't prove it.

And part of their "proof" is that generalist sportsmen in youth do better as adults than specialist sportsmen in youth. This is beyond stupid -- to be a generalist youth sportsman typically means that the parents have invested significantly more time, energy, and money, and it's pretty obvious that effort in related fields usually pays off well, and most sports don't run all year, and it's useful in physical endeavors to make your body move in different ways.

It is trivially accurate for them to mention that the possibility of burnout is a real thing, but it is also risible to discount the positive benefits of sustained attention and effort.