Churchill was never able to completely overrule the military leadership to quite the same extent as Hitler could. I admit that some of his decisions were plain wrong from a military standpoint. The most obvious was the commitment made to Greece. But contrary to popular opinion, in the initial stages, a British involvement in Greece was actually supported by the military establishment. It was most strongly resisted by the Greeks themselves, as a matter of fact, who appraised the likelihood of German intervention, if the British were allowed into the theatre. The Greeks were more or less extorted to allow the British into Greece by two things, the heavy casualties they were suffering (despite their successful defence), and a complete crisis in the artillery (and vehicles that they were using. They were mostly equipped with Czech weapons, with some Italians thrown in. By February, their stocks of ammunition were running dangerously lot, The initial negotiations with the British weer mostly about getting access to the vast quantities of captured Italian guns and ammunition that had been captured in the Desert offensive. But the British were not happy to allow this, unless British air and ground forces were also allowed in. This part of the negotiations were supported by the war cabinet. However, after the Yugoslav coup, it was assessed that German intervention was very likely. The war cabinet, was sharply divided, and the issue had to be decided by Churchill, who made the wrong choice, as it turned out.
There were lots of other decisions made by Churchill, that dont flatter him. On the other hand he was a prolific "ideas" man, for example, he was the inspiration behind the mulberries, and also pushed through the "Tiger" convoy.
Later, Churchill's interference was severely curtailed by the Combined Chiefs, which prevented the political intervention in the management of the war to a large extent. In Germany there was nothing to compare with this, Hitler was able to actually increase his control of operations, whereas Churchill's control decreased, as the war progressed