>Scholars don't blame the Ottoman anti-Semitism on economic malaise, but instead point to it being imported by Christian Arabs from Europe
So this was not a latent feature of Islam or Muslim culture, but an import from a more anti-Semitic culture (of course, the word Semitic here is not quite correct, given that Arabs are also Semites - I don't know why that word is preferred when the actual meaning being conveyed is anti-Jewish). The original poster I was responding to said this;
>the issue of anti-Semitism long pre-dates the establishment of Israel
Perhaps that poster only meant that anti-Jewish sentiment rose in the region a few decades previous, but the most common way I have heard of that belief, it comes from a "clash of civilizations" mindset that holds that the region has been rabidly anti-Jewish for many centuries.
Also, to your point that the Ottoman Empire only began declining in the 20th century, see https://www.britannica.com/topic/decline-of-the-Ottoman-Empi...: "But the grandeur of the Ottoman Empire did not last, and Süleyman’s rule was followed by a slow and arduous decline that spanned nearly four centuries."