Complex sentence: His reputation was of a stern disciplinarian who was one of the harshest and most effective whips, though this has been challenged by some arguing weaknesses and his system and the number of high profile rebellions during his tenure.
Split into simpler sentences: His reputation was of a stern disciplinarian who was one of the harshest and most effective whips. This assessment has, however, been challenged by some, who argue from weaknesses of his system, and the number of high-profile rebellions during his tenure.