I don't believe it -- although ideology makes explanations like that popular with a lot of people.

The cost escalations and bungling were well in progress before the TMI. The NRC streamlined the reactor approval processes in the 1980s by trying to separate the licensing of a standard reactor from the licensing of the site -- nobody took them up on the offer.

In the case of AP1000 builds both Sumner and Vogtle were held up for years because they were waiting for Chinese factories to figure out how to make parts, in some cases they never figured it out and they had to source them elsewhere. Factory modular construction was supposed to prevent bungling at the site but replaced it with bungling at the factory.

In theory the factories got up the learning curve and if somebody ordered another AP1000 it would be different, in practice the AP1000 is a Chinese reactor and the Chinese gave up on it for the Hualong One which there are (oddly enough) two designs for, which goes back to the designs the French were using back when they were building many plants on time and on budget... which is maybe a good thing, but they look pretty quick to move on to the Hualong Two and before they get up the learning curve on that one they'll be switching to the Three...

I'll agree that the Europe hired somebody who thinks like Amory Lovins to design the EPR and really did bungle the politics more than the engineering, but that's not the story in the US.

Regulatory requirements were definitely a real thing. One of the drivers was that nuclear companies were required by law to match the price of oil and any surplus profits from that had to be reinvested into safety and that set the bar for new safety requirements. What that meant was the 1970 oil crisis created a new level for nuclear safety beyond what was needed and that was locked in for future construction. The entire history of nuclear energy is one of bungled regulation and given the political power oil companies have had and continue to have, it’s not surprising given the existential threat nuclear posed.