This sounds like little more than pure speculation.

Based on the exact same factors the article very selectively chooses to highlight, you could just as well claim that it wasn't competition but a very high degree of integration that has made Europe so successful and that all the competition and war between states has just obscured this fact.

You could then go on and invoke the example of the United States to show that even deeper integration without too much internal warfare resulted in an even better outcome in terms of wealth.

This is nothing but fluff. You could pick and choose your variables to prove anything and its exact opposite based on that sort of reasoning.

What's the empirical basis for any of this? Why should we believe this theory and not some other theory? I don't see it.