According to Osho, yes—after Mohammed many great mystics arose, but orthodox Islam rejected them; figures like Bayazid Bistami were cast out and Mansur al-Hallaj was executed. Their living insight crystallized as a distinct stream called Sufism, unacknowledged by mainstream Muslims, and later diversified into multiple lineages, each carrying the essence of that rebellious, precious experiential truth.
Yes—many important Sufis came after Mohammed, like Bayazid and Mansur, but they were pushed out by orthodoxy and formed their own paths.