And he was discharged of his Duty as General in the middle of Battle of Yarmook, No doubt the finest General the world has ever produce but victory is never comes from one man, its always the collective effort of a whole Army/nation, That is exactly the point Omar Khattab RA wanted to make when he did that brilliant and daring decision. Putting the example in the matters of our Army who would like to compare themselves to those imaginably great people, a Leader appointment by the nation can't sack/appoint the General, that tells a lot about our current/past/future situation as a country/nation.
A man once come to Hazart Ali RA after the battle of Jamal, Ali RA was sad on the affairs of Muslim and that man said to him, why is that in your term as Khalifa are these strife and tribulations ? and not in the time times of Abu Bakr and Umar RA to both, he said when they were Khalifa they were ruling over man like me, and when I become Khalifa I am ruling over man like me... We are blessed that we had access to the lives of these great people and how they lead the Muslims from the far end of Europe to the Modern day Pakistan with Justice and Equality and yet we learn nothing from them.