Being a great leader does not necessarily mean being a great general. I would like to make a comparison in the case of Churchill with George Washington, in view of his lineage I hope the Americans among us will not be offended.
Washington - Statesman:
As the Commander in Chief of the Continental Army the services and achievements of George Washington are unique in the world's history. He was much more than the Commander in Chief. He was the one necessary person, whose calm, unswerving, determined sense of patriotic duty to country, and ability put real backbone into the Revolution and kept it from collapsing or merging into a civil conflict, under the hardships and unexpected privations encountered during the eight years of war. Without General Washington at its head it could never have succeeded. His faith in the cause and his devotion to the ideals it embodied made him the symbol of America -- the spirit of the Revolution.
Washington - General:
While Washington was in overall command of the entire American war effort, simple logistics and the limitations of that era prevented him from personally managing the course of events in all the colonies. Consequently, he was in direct command of American troops in only a few battles of the Revolutionary War. He lost most of them. In fact, among the consequences of Washington being driven from the battlefield were the losses of America's most populous city (New York) and her capital (Philadelphia). Then and now, critics point to these sobering facts as a reminder of Washington's failures as a military commander. They go further, arguing that even his successes were relatively small-scale affairs (Trenton and Princeton) and resulted from the overconfidence or incompetence of his enemies as opposed to any brilliance on his own part. And they point to Yorktown, the crowning achievement of the American Revolution, as the best evidence that America could not have won the war without French assistance.
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So I would rate both Churchill and Washington as being great leaders, but lousy generals. The two not being mutually exclusive