That research was of candidates who had experience in competitive programming competitions, and IIRC it didn't show that they did worse but that they didn't do

That research was of candidates who had experience in competitive programming competitions, and IIRC it didn't show that they did worse but that they didn't do better. There's a restriction of range effect at play here: if you look at the top "GTTQ" quartile, you're not going to see it have a huge effect in performance within that range (and the factors you mention would be far more predictive of on the job performance). But the relevant comparison isn't between how well actual candidates who barely got in perform versus how well candidates who steamrolled the GTTQ questions perform; the comparison is between the hypothetical performance of the candidates who didn't get in because they failed the GTTQ questions and the actual performance of candidates who did get in because they did well enough on GTTQ questions. For that you'd get a much stronger signal. Though it would be interesting for Google to arbitrarily give offers to 1% of people who flunk the existing interview process just to track how well they perform on the job; that would give the world some really neat metrics to look at. (At the cost of giving everyone they hire even worse imposter syndrome.)