A legendary portfolio strategist just dropped an eye-opening result: his long-short approach managed to double S&P 500 gains over just eight months. Here's the kicker—he did it by exploiting the gap between a specialized US equity ETF and the broad market index. It's a direct challenge to the conventional wisdom around passive index investing. The strategy reveals something important: there's real opportunity when you dig beyond what everyone else is holding. Whether this works going forward is another story, but it shows why some pros aren't content sitting with standard index returns. The divergence between different index methodologies might be bigger than most assume.