Is the SAT or ACT a particularly good test of intelligence? Smarts, maybe, but I've met a lot of extremely intelligent, talented people who are not particularly "smart" by these measures.

You can practice and take classes that teach you how to do well on the SAT/ACT. No guarantee that you'll ace it but you'll do much better if you know the strategy behind a perfect score.

This is one of the reasons people with more resources do much better on these tests - getting test-specific tutoring, taking prep classes, etc. will significantly raise most people's scores. The tests are much closer to measuring "How good are you at taking the SAT/ACT?" than some kind of unbiased "How brilliant are you?" measurement.

As opposed to all those other academic tests where resources and preparation make no difference?

Once you are in school, perhaps with a scholarship, you have many more resources and time to prepare, to compete with classmates. That's the point - just getting into the school is filtering out students, even those that demonstrate achievement and commitment in other ways (i.e. grades).

I don't understand what that has to do with intelligence? Rote learning doesn't make you intelligent. Again, OP specifically said "if you can't complete on intelligence" and then went on to draw a link to "activities" being bullshit, and therefore a not a measure of intelligence. That makes no sense at all.