The selection bias might not be relevant if the message is not

"slack around as kid, it will make you great later!"

but

"prodigy youth doesn't guarantee greatness later, as well as non-prodigy youth doesn't prevent you from becoming grat later".

Graduated with a 1.7 GPA and a 32 on the ACT. My parents were a little dismayed.

I'm not sure we should romanticize ADHD, which is what you call that region. If those people could be high SAT and high GPA they would prefer it. Signed, someone in that region.

What does the reverse imply? High GPA, low SAT?

IMHO, it's MUCH more common in sciences though, that someone that is expert-level in one field comes into another and thinks they CAN solve a long standing problem in that field quite easily, and then repeatedly falls into all the pitfalls / traps that others in that field learned long ago to avoid (aka Dunning-Kruger). You know, "chemistry is just applied physics", "biology is applied chemistry", etc.. Sure, it's true in one sense, but... No one calculates the wave function of an elephant, for example.

One of the benefits of generalism / learning multiple fields (IMHO, again) is that you realizes that special abilities / skills don't necessarily translate well from one field to another. For example, learning to play the violin is very different from, say, playing billiards, yet becoming good at either one involves learning subtle manipulations of basically similarly-shaped pieces of wood. By involvement in multiple fields, you learn to be careful NOT to bring your "everything is a nail" mentality with you from one field to the next.

Gretzky is well-known for saying he thinks kids should play multiple sports and avoid hockey in the summer, like he did (IIRC) - he mentioned soccer, etc.

in contrast: the sport i know best, hoops, a common pattern for generational players is for them to be late bloomers because they grow up short, developing skills and competitive toughness, then get lucky and grow a half-foot late in puberty