In any case, it is likely that the globalization of the industry has (a) increased the quality of African national teams relative to European national teams; and (b) reduced the quality of domestic leagues in African leagues relative to club play in Europe.
(a) is definitely true; (b) is probably also true, but the key words are relative to club play in Europe. I don't see why that, rather than absolute quality, is the best metric. I'm surprised an economist (even a heterodox trade skeptic) would gloss over the distinction. It's not the case that there are a fixed number of good soccer players out there that European clubs are going down to Africa to lure away. Talent, to some degree, is a function of capital. Because soccer is such a big business in Europe, European clubs invest a good deal of money--in the form of sports academies, facilities, equipment, and so forth--into developing the game in places like Africa (much as American baseball teams do in Latin America). As a result, I'd bet (though like Rodrik I'd like to see some data on this question) that in absolute terms the average skill level of players in African leagues has probably gone up since the pre-globalization era, even if the best African players now end up in Europe. So the unhappy fact that fans in developing nations no longer get to see their best players in their domestic leagues is mitigated not only by the fans' ability to see those players with top European clubs, but likely also by the reality that there are still lots of good players--particularly young ones--at home who are far better players than they'd be in the absence of European soccer investment in Africa. (Though, as our fearless leader noted in a chapter of his book, that investment has failed to alleviate other problems, like rampant corruption, that plague domestic leagues in developing countries.)