Colleges don’t use Subject tests and AP tests in the same way.
SAT Subjects are used in the same way as the SAT but provide a better indicator of academic achievement in what is presumably the student’s best subjects.
Foreign Language SAT subject tests are also the only ones used like AP, as a proxy for placement and college credit provided a high score is achieved (that score varies depending on the university).
Some universities are “test flexible”: they allow you to take either M1 or M2 + one humanities + one of your choice, as a replacement for the SAT. This means, if you’re really strong at two subjects beside English/Reading, you can submit scores in your strongest areas.
AP’s count, first, for the class the student takes, as an indication of rigor and willingness to challenge yourself while balancing things out properly (“Ap junkies” aren’t especially well-regarded - those kids who take every AP but the kitchen sink just because they can, but don’t seem to have a rationale for their choice).
AP scores, when the guidance counselor presents the range and average of AP test results, are also a useful indication for adcoms. Scores aren’t always provided by applicants but when they are, they should be passing, and for the most selective universities, a 4 or 5 is expected.