And while any medrash might refare to arabs as a race, islam as a religion started around 1,300 years ago. That will be at least 500 years after any medrash.
Not ‘any’ Medrash. Many Midrashim were written or finished in the time of the Geonim. The Medrash in Nasso speaks about the Cristians and Arabs claiming that they have the Torah. That is why we didn’t write Torah Shel Bichsav, so that they shouldn’t lay claim to that as well, says the Medrash. The Kamarna writes that the Raaya Mahimna in the Zohar Hakadosh was written by a Gaon named Shalom.
Who wrote, “Ha D’reb Ashi Bedusa Hi”, if Reb Ashi made the Gemara? The Tzemach Dovid writes that it was written 70 years after Rav Ashi was Niftar.