Regardless of whether or not it is halachicly acceptable, I cannot see how the “oy” sound can possibly be the original authentic sound for a cholam.
1. Many people who pronounce the cholam as “oy” are not consistent in doing so and often switch back to “oh” even in the same sentence as another cholam and even more often by Hashem’s name, for some reason.
2. Sefardim and Germanic Jews all say “Oh”, though the sound is sometimes closer to a kamatz by a Sefardic Jew and more like “ow” by a Germanic Jew. But there is no extra “yud” in there any way you slice it.
3. That most women are taught “oh” and not “oy” is fairly indicative which is the original and which has been somehow adopted by a “yeshivish” crowd. If “oy” were the “real” sound then you would think that women would be taught to pronounce it that way, too.