Complex sentence: The original plans had not, in fact, called for such a high first drop, but the construction of the Mean Streak at Cedar Point prompted design changes that some suggest have contributed to the high rate of injuries in the park's early years.
Split into simpler sentences: The original plans did not include such a large first drop, but construction of the Mean Streak at Cedar Point prompted the design change. Some have alleged that these changes may have contributed to the high rate of injuries in the ride's early years.