I read the introduction as referring to the effects on those regions that gave up their status as members of the empire, rather than what you’re saying.
The author fails to understand that decolonization can be a pretext for continuing exploitation of foreign territories while abandoning the nominal moral obligation to develop them. In the counterfactual where the US maintained control of these countries, they would not have been developed to first-world standards, they would have just been exploited overtly.
Since you state this so confidently, surely there's an example in our current timeline where it happened this way, right?
Like how is there a section on Cuba that does not mention the American embargo on Cuba for the past 50 years? How can we take this analysis seriously?