Nuclear fission power apologists frequently make a claim like this when trying to establish why costs are so high (it doesn't necessarily explain why cost overruns are so high, as presumably the regulation set is known at the time of project initiation).

If this were the / a major factor in cost competitiveness, we'd expect to see much higher uptake of nuclear fission power plants in places where, as you might say, those things are disregarded (to varying degrees).

I don't believe that's the case, but can't find convincing data one way or the other.

I wonder if there are examples of massive cost overrun / delayed commissioning nuclear fission plants - say Hinkley in the UK - that could be pointed at to substantiate the 'process and regulatory approval' costs, where those process and regulations changed after the initial cost calculations.