"Reasonable"? The idea was popularized by Gurdjieff, G. I. who was a mystic teacher. There is nothing reasonable about it. not a single wiff of actual truth, just rebranded new age woo for corporate elite. I may sound harsh but from what I've found in my own personal research it is much of a religion as scientology and as much science as astrology.
https://www.integrative9.com/enneagram/history/