You're not exactly wrong, nuclear is a terrible pairing with renewables for the reasons you listed, but it's still probably cheaper than batteries under extreme conditions, which is something we do have to deal with.

90% renewables is cheap, 99% is more expensive, 100% is really really expensive. Batteries are great for 24 hour storage, but storing energy for longer starts to become uneconomical and to hit 100% you have to buy enough capacity for the absolute worst case scenario. Anything that baseline nuclear cuts off from renewable demand is potentially cheaper than the theoretical worst case 1% of renewables (eg if there's no wind and it's cloudy mid-winter, how much solar/wind do you need to power the country, or how much battery do you need to maintain power for weeks under these conditions?).