I'm not sure what's been debunked. The US does not have the construction capabilities of 1970s France. And for that matter, neither does France, as is being proven in Flamanville and in Olkiluoto, Finland.
Perhaps we can invite Slovakia or Russia to build in other countries, but there's no knowing if they could train local workforces accomplish what they have.
I suspect the real reason is "maybe turning profit-skimming by intermediate layers of management into an art-form, makes any large-scale project-costs trend to infinity".
HS2 spent ungodly sums on "consulting" and management fees to do stuff that, back in the day, would have probably been carried out by a couple of commandeered civil servants. But I'm sure all their Word reports have nice headings and lots of "holistic" something.
