What matters more: AP or well-roundedness?

"You can’t compare number of APs with students of other schools. "
of course you can. Admissions officers certainly could, but they dont.
BUT students dont KNOW that they dont- they assume it is “one big horse race” for each college and the “student with the most AP’s wins”. Hence the “mania” to increase the # of AP classes, regardless of whether it makes sense or not for the individual student.
I’ve been on CC for 13 years and this nutty AP race just keeps gets worse and worse each year, and the ones who pay the price are the students who fall for that trap.
So OP- stick with the HARDER 4th year NON AP foreign language class, rather then an EASY AP math class.