The removal of Warren seems to be a defining event in how some have come to view Sheridan, so that I have searched around to try and get as many perspectives on this as possible. Below is an interesting commentary on Sheridan's actions, because it separates the "fairness" of the removal from "right" to do so by the discretion left to him [Sheridan] by his commander, Grant.
Far more interesting is the debate over the relationship between Sheridan and V Corps commander Gouverneur K. Warren. Warren had enjoyed an uneven record as a corps commander and had poor relationships with Grant, George G. Meade, and Sheridan stemming from the first weeks of the Overland Campaign. These feeling resurfaced when Sheridan learned that he would have to settle for working with Warren rather than being given Horatio Wright's VI Corps for his swing around the Confederate right, although Wright had fought ably under Sheridan in the Shenandoah Valley. One suspects that Grant took the unusual step of authorizing Sheridan to relieve Warren on the spot should Sheridan deem it necessary in part to calm Sheridan's irritation about having Warren instead of Wright. In the battle that followed, Sheridan found fault with Warren's performance, and relieved him of command. Believing that Sheridan's action was unjust, Warren spent the remainder of his life seeking a court of inquiry, which was blocked by Grant as general and president and did not take place until after Grant returned to private life. Whether Sheridan was fair is one question, but he clearly had the right to exercise the discretion left him by Grant, and he preferred to have V Corps commanded by Charles Griffin. Given the lack of confidence several generals had in Warren, perhaps it would have been wiser to relieve him of field command during the previous winter. To this day both Sheridan and Warren have their partisans
https://cwcrossroads.wordpress.com/2015/04/01/april-1-1865-five-forks/