I completed this one on normal difficulty.
Do not make the same mistake I did by pulling back all of your forces to this island thinking you can make a last stand, because you will still fail. There is a further island to the rear connected to the main city by two bridges where Notre Dame rests. Specifically, the Red Palace and Guild Hall at the back of your base must not fall or you will trigger the fail state. If the city is destroyed, you fail the mission. All you have to do is survive until the enemy has depleted itself over the course of 10 waves. This is purely a defensive mission there is no need to plan a counterattack.
It’s a tough fight, but rest assured you’ll come out on the other side. This guide will explain how to best make your way past the Siege of Paris in Age of Empires IV. In the second mission of the campaign, they are pushed all the way back to Paris and must mount a hasty defense behind its mighty stone walls. Although confronted with inferior English numbers, the mighty French army is decimated by the enemy’s fearsome English Longbow. In the second campaign of Age of Empires IV, you take control of the French army during the Hundred Years War.