Its easy to forget that Attlee was Churchill's deputy during the ww2 and that the various labour leaders who led govt departments (Morrison, Gaitskell etc) or in opposition (e.g. Bevan) in ww2 established their legitimacy to govern post-war. Similarly When Churchil was re-elected back to power in 1951 he recognised that Attlee's government key achievements like the National Health service (whch Churchill had originally fiercly opposed) were for the benefit of the country and did not dismantle them. Attlee and Churchill in some respects had combination of both war and peace time leaders that isnt always recognised.
I am glad you mentioned Churchill here. I recently read a few biographies about him, and he appears to have had just the leadership capabilities needed to win the war, but those same leadership capabilities didn't make him as successful a leader during peacetime.
I often think that war leadership is much easier than peacetime. You have a clearly defined goal and not too many competing priorities. Peace is much more complex.
This is one benefit of democracies. People can form alternate leadership structures with different strengths and focuses, without them trying to wrest power at unpredictable times.
Worth noting that in a parliamentary system, the voters does not select the prime minister directly. Churchill was popular as a leader, but he was the head of a wartime coalition which ended towards the end of the war.
Even Churchil, considered a hero in Britain after WWII, lost the next election badly to Atlee, as people were looking for a peacetime leader.
The good thing is Atlee setup the NHS. So I guess peacetime leaders are important after war.