The military still uses it because it is highly predictive. They also have a hard cutoff at the bottom which wasn’t always the case (see McNamara’s Folly for the history of when the army accepted literally retarded people - it didn’t end well). We also see a very strong correlation between eg IQ and occupation.
The U.S. marine corp promoted its first black 4 star general this year. I don’t think it’s the shining example of a race-blind institution, at least as far as leadership is concerned.
You are cherry picking data. The US military has historically been far more progressive than the country as a whole. It integrated in 1948 - long before the voting rights act or the end of Jim crow. We had a black chair of the joint chiefs long before we elected a black president. Rights and privileges were extended to gay members long before they existed elsewhere.
It is a legitimate metric of *something*.