I'm pretty well acquainted with the situation. I'd recommend this research on the subject that are mainly applicable to building transit, but I expect the same observations are generally true in other megaprojects: https://transitcosts.com/

From the executive summary:

In our New York case, we show examples of redundancy in blue-collar labor, as did others (Rosenthal 2017; Munfah and Nicholas 2020); we also found overstaffing of white-collar labor in New York and Boston (by 40-60% in Boston), due to general inefficiency as well as interagency conflict, while little of the difference (at most a quarter) comes from differences in pay.

Projects in the anglosphere are overstaffed for both design and construction, and there's little evidence to show that there are better outcomes. Costs in Sweden are 20% those of the US, and yet you'd be hard-pressed to claim that Swedish workers are undercompensated or produce shoddy work.

As for "to spec", the SF Central Subway, which opened 5 years after it was planned to and cost 3x as much as initially forecast, had delays because the contractor attempted to get away with using sub-standard steel. In order to save time and open sooner, the city kept some of the sub-standard rails in use in lower-traffic areas.