Chief, it’s the belief that Torah needs something to complement it that is considered apikorsus by gedolei yisroel. Rav hirsch wrote that the chochmos are the handmaids of the Torah, they serve it, they don’t add to it itself. They add to OUR understanding of the Torah , not due to the Torah lacking anything – see maharsha on the gemaros that deal with refuos…hafoch bah, toras Hashem temima, etc…the chisaron is in us, that we cannot access everything from Torah study alone, but we need to learn math and science from the outside to understand Torah better.
Where modern orthodoxy split off, and this was not the view of rabbi yoshe ber soloveitchik, rather it was the view of norman lamm, Bernard revel, and Samuel belkin, who were the ones who brought the idea of something besides Torah having value. Rabbi yoshe ber had his opinions which were not agreed upon by the gedolei hador, but they were nowhere near the apikorsus and insult to Torah the likes of the others brought into American jewry.
Lf course, that group was not the original source – the idea of there being something of value besides Torah was popularized by maskilim in Europe. It was their bread and butter.