Probably Stalingrad and the Kursk salient were the turning points in the European sphere, Midway in the Pacific. El Alamein in Africa was also important as that led eventually to the invasion of Italy.
Without these i would argue D-Day would not have happened when it did.
I am not saying Churchill wasn't important, i am saying his importance is exaggerated because of the way history is taught in the UK. We have a romantic view of history that has led to myths being formed and idolatary is a dangerous weapon exploited by the far right. If history is to be taught then teach it properly so that people can understand the role of Churchill warts and all, why his failures like Gallopili and Narvik, his past as a an officer in the Boer war, his experinces in the Anglo sudan and Indian confrontations all moulded him as a man. Then people can make a proper value judgement on him as an historical figure. Knowing he led the UK in WW2 is only a small part of his story, he was a man who divided the nation, he sent troops against people on strike for instance. Both my grandads who were from very different social and political backgrounds hated him. One of my grandads was a desert rat and he thought Churchill was a butcher. my other grandad was one of the very few who was too young to fight in WW1 and too old to fight in WW2 and he hated Churchill because he was a Tory and he hated all the Tories.
If we taught history properly then people would understand or maybe at least have a better understanding of his relevance, yes he was a great man who led us through the darkest times, but he was inherently flawed and if people knew about his flaws then they may accept the good he did more readily as it would be in context.
Its this romantic notion of British Imperialism that is being questioned at the moment, we are a country used to being seen and acting as we are exceptional, that for me is the crux of the matter. We have these myths we rely on to still claim the Great is in Britain and everything indicates that is false, we are still a good country, which enjoys a privileged and decent standing in the world but we are not the country of historical myth.