Yes, this seems to me like mostly FUD, because there is no line of reasoning to be found (I read it on outline.com). It says it takes too long to innovate, without any concrete evidence, afaik there are many innovative reactor designs waiting to be constructed. Maybe not next-gen, but better than past ones that need to be shutoff at some point. Also the old design PWRs still work well and can be constructed today within a few years, so definitely worth pursuing.

Economically more viable than burning stuff that literally comes out of the ground and there is near endless supply but destroys the climate? Definitely not, but neither are renewables. The economy won't safe the climate.

Arguments against nuclear would probably be fuel availability/harvesting and safety.