The point isn't that skin in the game causes better decision-making, the point is that the losers exit the gene pool. If you walk into any restaurant in the United States, you can bet the food is of better quality than that of a Soviet-era cafeteria. The difference? One group has skin in the game and must compete or die. One group doesn't. Skin in the game ensures the health of the restaurant industry (as measured by, say, quality of food), not the health of any one restaurant.
As for your assertion re: experts in "closed" vs "open" systems, the issue is less one of "open" systems requiring humility, and more that "open" systems are statistically filled with BS artists. Why? Because they don't have the filtering mechanism that gets rid of those people. A fake dentist can't pull the wool over patients' eyes for long, but a macroeconomist can do just that for his entire career.