There is a school of thought (with some validity, though I think it lacks nuance) that points out that the early Roman Empire, the Principate of Augustus until the Dominate of Diocletian, tried to empower the Senate. The Senate had its set of provinces, the emperor his. The cursus honorum was still used to track and groom administrators and leaders and the senate's support (balanced against the army and the people of the city of Rome generally) still legitimized the emperor. But over time, goes this line of thinking, senatorial attention and interest fell away somewhat from administrative and managerial responsibilities and turned more into a social/politicking club, and the emperor "naturally" picked up the slack.

There is an element of bias to this, and it often reveals a political preference of the author, but it's not without some merit.