When markets are top-heavy and expensive, like in 2000, the concentration risk of market-cap weighting is severe. In the 13 years after the dot-com peak, while the S&P 500 went nowhere, its equal-weighted version doubled, highlighting a powerful de-risking strategy.
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Investors' equity allocations are high, not necessarily from new purchases, but from strong market performance. This passive 'drift' creates a significant, often overlooked, concentration risk. This means many portfolios are more exposed to an equity drawdown than their owners may realize, necessitating a review of diversification strategies.
Today's market is more fragile than during the dot-com bubble because value is even more concentrated in a few tech giants. Ten companies now represent 40% of the S&P 500. This hyper-concentration means the failure of a single company or trend (like AI) doesn't just impact a sector; it threatens the entire global economy, removing all robustness from the system.
Market-cap-weighted indexes create a perverse momentum loop. As a stock's price rises, its weight in the index increases, forcing new passive capital to buy more of it at inflated prices. This mechanism is the structural opposite of a value-oriented 'buy low, sell high' discipline.
The S&P 500's high concentration in 10 stocks is historically rare, seen only during the 'Nifty Fifty' and dot-com bubbles. In both prior cases, investors who bought at the peak waited 15 years to break even, highlighting the significant 'dead capital' risk in today's market.
The performance gap between market-cap and equal-weight strategies is not random; it's cyclical and can last for over a decade. While market-cap has dominated recently (winning 8 of the last 11 years), this was preceded by a period where equal-weight won for 13 of the prior 15 years. Recognizing these long cycles is crucial for strategic allocation.
The underperformance of active managers in the last decade wasn't just due to the rise of indexing. The historic run of a few mega-cap tech stocks created a market-cap-weighted index that was statistically almost impossible to beat without owning those specific names, leading to lower active share and alpha dispersion.
The current market is not a simple large-cap story. Since 2015, the S&P 100 has massively outperformed the S&P 500. Within that, the Magnificent 7 have doubled the performance of the other 93 stocks, indicating extreme market concentration rather than a broad-based rally in large companies.
After years of piling into a few dominant mega-cap tech stocks, large asset managers have reached a point of peak centralization. To generate future growth, they will be forced to allocate capital to different, smaller pockets of the market, potentially signaling a broad market rotation.
While indexing made competition tougher, the true headwind for active managers was the unprecedented, concentrated performance of a few tech giants. Not owning them was statistically devastating, while owning them reduced active share, creating a no-win scenario for many funds.
Market cap indexing acts like a basic trend-following system by buying more of what's rising. However, its Achilles' heel is the lack of a valuation anchor, causing investors to over-concentrate in expensive assets at market peaks. In high-valuation environments, almost any other weighting method, like equal-weight or value, is likely to outperform over the long term.