The counter point to that would be analysis on "sub-imperislist" countries and regional blocs, of which many Marxists, including Amin, have covered over the last 50 years. But I don't think that they will be able to understand it if they can't understand imperialism first. Because, well, most sub imperialist blocs tend to align themselves with Western interests in the bigger picture at some point or another, as the global capitalist imperialist system led by the triad of the United States, Western Europe and Japan is the dominant imperialist force in the world.