Re: scores not being as good a predictor, there is this study involving SMPY:
https://www.cnbc.com/2017/11/10/longest-study-of-genius-kids-reveals-what-it-takes-to-be-successful.html
There was a Nature article last year on the same research, going into a bit more detail:
https://my.vanderbilt.edu/smpy/files/2013/01/Article-NATURE-2016.pdf
Although I disagree regarding skipping grades, based on this along with the other results stating the importance of gpa, Massmomm’s view sounds like a prudent assessment.