I wouldn't expect that. Algorithm interviews as they're practiced tend to favor memory abilities and not cognitive. It's hard to come up with standard algorithms on the spot if you haven't been exposed to them.

I do know that cognitive abilities and long term memory abilities aren't correlated. Cognitive abilities and short term / working memory are positively correlated though.

I work at Google, based on personal experience I would say it does a good job of setting a minimum bar in terms intelligence and coding ability. However, it might reject some people unfairly.

A little bit of preparation helps a lot, but beyond a certain point preparation doesn't help anymore. All interview questions require solving a new problem in the interview itself.

Depending on the interviewer and question, the difference between a hire and no-hire recommendation can be quite marginal. There is a huge luck factor involved.

With or without months of preparation on some of the exact problems interviewers use “grinding LeetCode”?

The trick here would be separating high IQ people who have prior algorithmic experience from those who do not, because that's a much bigger influence on performance.