For anyone that comes across this post and has a child with similar weaknesses, I thought it would be helpful for me to update to give others hope.
My son's fine motor skills, after years of being significantly delayed and needing regular therapy, have suddenly completely caught up and become above-average with no further need for therapy. It was always asynchronous development (as we hoped), but he still needed help to get through it.
Also, I found out that he was given two processing tests during his IQ testing, one reliant on fine motor skills and the other not. His FSIQ can also be calculated with the alternate processing score and if so he meets Davidson's criteria for admission. Further testing done by his school (cogAT) has given similar results. He has met local Davidson Young Scholars (instant bonding) and we have been advised by their parents to apply so it's something we plan to do in the future when life is a little less busy.
Now that his fine motor skills are above-average, he has absolutely no problem with his grade-skip, other than that it's not enough anymore, and an additional grade-skip has been suggested to us by school officials.
So, if anyone has a child that also tested as disabled by their state and needed years of therapy, there is hope, because sometimes asynchronous development looks like this.
