It's fatal to his position because if it is proven to be false, if it is seen that the Jews suffered at the hands of the Arab Islamics like they suffered at the hands of European Christendom and post-Christendom (the anti-Semitism which formed out of the Enlightenment - Voltaire, Fourier, Proudhon, Goethe, etc.), then it would undermine the totality of his argument. It would illustrate that the Jews could never trust the Arab Islamics with their sovereignty and hence any claims that as living as a minority under Islam they would be well treated, respected, etc, would be undermined. By agreeing with my assessment of the failure of his historical comments you have admitted the failure of his position whether or not there is any substance to his Torah claims.
In your opinion. His religious arguments do not change. Moreover, the historical references you site are not in the region of Palestine by and large but in Syria, Morocco and on the African continent IIRC. And furthermore, well after the Moslem empire had fallen except for one recorded period around the beginning of the empire.
Furthermore they don't refute what he actually said as opposed to what you (and I) apparently thought he said.
And in Palestine alone our grandparent have testified to the fact that the Muslims and Jews lived in peace and harmony up until the advent of Zionism.
He's quite specific about the time periods he speaks of:
Only blind dogma could at this date see Israel as something good for the Jewish people. Established as a so-called safe haven it has consistently over the past five decades been the most dangerous place on the face of the earth for a Jew to live. It has been the source of tens of thousands of Jewish deaths, of families torn apart and has left a trail of grieving widows, orphans and friends in its wake.
I think I mis-spoke. His so-called history gaffes were perhaps not made at all.