Long philosophical tradition gave Western monotheists an edge in the first world debate

Evidence

You will scarcely want to hear the arguments that can be adduced in favor of monotheism on the one hand and polytheism on the other, and I need scarcely say that in William’s account at least the monotheistic arguments had decidedly the better day. Nor is this unlikely. William could speak with the authority and precision of a long philosophical tradition; his enemies were tied up in complicated genealogies of Gods in heaven and Gods on earth, and they were unable to give a clear answer to the question of God’s omnipotence. Finally they committed themselves to the view that no God is omnipotent, and at this William won the sweet triumph of a loud laugh from the Moslems among the spectators. — R. W. Southern, Western Views of Islam in the Middle…, 312

Related

• Medieval Christians assumed Muslims shared common ground on monotheism (similarity 0.82)
• Islam’s early religious rivals sometimes praised its monotheism (similarity 0.79)