There's also a problem with your line of thinking: you are not a child. You do not have the neuroplasticity they do. Their brains are learning in ways that we simply cannot any longer; it' a real apples:oranges situation.
Neuroplasticity as a concept is challenging but even when Torsten Wiesel was sewing kitten and cat eyes shut the adults could adapt. And the claims that the kittens rewired more are problematic.
The neurons originally attuned to the closed eye did not acquire new functions, they heightened their response to the input from the open eye.
The responses were always there. Just at low levels.
Free time to to dedicate for building tactic knowledge is the main limiter for adults and not hard wiring.
https://solportal.ibe-unesco.org/articles/neuroplasticity-ho...
The general argument that I hear which is true (from all I've seen and read) is that neuroplasticity is greatly reduced in adults as compared to children. There is a period in early childhood where brains are incredibly flexible and adaptable, and as they age they continuously lose that ability until the majority of it has been lost by adulthood.
It doesn't mean there is zero in adulthood, just that it is very small compared to childhood.
I think you're arguing against something nobody really says.
The easiest example for me is learning guitar - I started when I was 5 and got pretty damn good over the years. It would be difficult to repeat that now in my 30s, but at least part of that difficulty would be because I can't really devote 3-4 hours a day nearly every day to it like I did as a bored kid out in the country. To be clear, I'm sure the differences in neuroplasticity come from both behavioral and neurological differences. It's just fun to think about how much is set in stone and how much could theoretically be "exercised" so to speak, and how much of the neurological changes are actually due in part to the behavioral changes as we age.