It was one part of it. The second part of it is the supply was heavily constrained. Countries around France (e.g. Italy and in some parts of the year Switzerlan

It was one part of it. The second part of it is the supply was heavily constrained. Countries around France (e.g. Italy and in some parts of the year Switzerland etc.) depended on that electricity too. So when it was gone it really screwed everything up. You are correct that gas is the highest priced and sets the price of all electricity, but it simply wouldn't have been used as much if french nuclear hadn't failed. That's how merit order works.