The correct comparison of the growth of Islam and Christianity in the Middle East between 300 and 1500 CE is:
During this time, Islam became the dominant religion in the region. Christianity was less established in the Middle East during this time, but its influence was still felt during the Crusades.
This statement accurately reflects the historical context: Christianity was established earlier, dominating the region for several centuries, particularly during the Roman Empire and up to the rise of Islam in the 7th century. After the advent of Islam, it rapidly became the dominant religion, especially following the Arab conquests. By the time of the Crusades (starting in the late 11th century), Islam was well-established and influential throughout the Middle East, while Christianity was primarily represented through the Crusaders and other minority Christian communities.