I think this theory's wrong.
The long-term trends in the economy don't follow a steady cyclical pattern; they're influenced by events.
For example: There was a long-term economic upturn, especially in the U.S., after WWII. Not because of a Kondratieff wave, but because a lot of means of production were destroyed in Europe (resolving the overproduction crisis), and because the U.S., as the victor, emerged from the war able to dominate the world market.
This lasted until Washington's competitors were able to rebuild...starting a long-term period of, at most, slow growth. This began with the '74 world recession.


