They are saying economics is the primary weakness i.e. nuclear costs more than renewables even if you don't have fancy cooling methods that would increase the cost further.

Well no it isn't, this problem is so small that it's not even worth installing any additional cooling method. It's also the lowest consumption period of the year, making the problem even more irrelevant as some plants are already offline for maintainance anyways.

And since the poster didn't knew that, I'm not sure the cost analysis holds up.