You are giving short shrift to the support and alliance that many Jews made with the Muslims. Take a look at the history of Spain and the history of Jews as administrators for the Muslims over the Christian population.
Moslems and Christians swapped principalities back and forth and were loathe to do more than allow Jews into the castle to read and write stuff for them.
The Jews allied themselves with Muslims for the very logical reason that Muslims of the time treated them much better than Christians did.
Crusaders slaughtered Jews in Europe and the Middle East for equally logical reasons. While the Pope and kings may have had the geopolitical motives discussed by the author, most of the Crusaders intended to just kill the enemies of God. Why travel all the way to Palestine to kill Muslims when Jews, equally the enemies of God, are right here in Germany?
The author is, however, absolutely right about the counter-attack nature of the Crusades. In fact, the Crusades were an incorporation of the idea of jihad into Christianity. That this took 400 years to occur is a result of the fact that jihad just doesn't fit well into Christianity.
The author also leaves out that the Crusades were a minor irritant on the edge of the Muslim world. Most Muslims were unaffected and unconcerned.
The Mongol invasions during the same time were catastrophic, dang near destroying Islam.
An example; When Jews resettled in Thessaloniki after its capture by Moslem Turks they were given and they took the properties of Christians who were then sold into servitude by Muslims. They cooperated closely with the Muslims there to maintain the misery suffered by Christians.
Until the Christians in Spain did the right thing and took their country back.
Muslims in Andalusia co-opted all minority religions. This included Catholics in Arian areas and Arian christians in Catholic areas. Jews accepted Islamic overlordship because they had no choice and because many Vandal warlords in Hispania were pursuing policies of either driving out Jews or forcing conversion.