I don't think that's necessarily to the detriment of the argument. This is how knowledge is created in fields which are difficult to quantify, but I appreciate your critical outlook on his method. Either way, his writing is very clear, founded on historical data, and aims to offer a practical understanding of the complex contemporary world. My qualm would be that the view that human history is bound to keep repeating is somewhat cliché, as I'd like to believe we can learn from it. Naive, yeah, but maybe books like these are the means to just that. Doubt US policy makers read it.

I would also argue he does go as far as he can to present his "data" in a systematic manner to infer some tangible knowledge. In an era when we're so used to most science being based on mathematics, the only evidence / repeatability of an experiment / theory / hypothesis (which is what his model is) lies precisely in how much you believe his method, and it's not an easy text to argue with given his conciseness.