The U.S. equity market is increasingly being driven by a narrow group of companies, while a large majority of individual stocks have failed to keep pace with the S&P 500 over the long term. Data from Trivariate Research show that only about 23% of the largest 500 U.S. equities outperformed the benchmark over the 10 years through August 2026, highlighting how unusually concentrated long-term market leadership has become.

Long-Term Outperformance Has Narrowed Sharply

The latest data point to a significant deterioration in the breadth of long-term equity-market performance. Among the top 500 U.S. stocks, only approximately 23% outperformed the S&P 500 over the past decade. The figure has fallen steadily from levels seen during earlier market cycles, when a substantially larger share of individual companies was able to outperform the benchmark.

The trend is not confined to the largest companies. Across the top 2,000 U.S. equities, only about 22% outperformed the S&P 500 over the same 10-year period. According to the source data, both measures have more than halved over the past decade, indicating that the challenge is broader than simply the performance of a handful of mega-cap stocks.

Index Performance Is Becoming More Concentrated

The significance of the data lies in the widening gap between index performance and the experience of the average stock. When only roughly one-quarter of companies outperform the benchmark, the index’s long-term gains become increasingly dependent on a relatively small number of successful businesses. This dynamic can occur even when the overall index continues to produce strong returns, because the market capitalization weighting of the S&P 500 gives its largest constituents a disproportionate influence over aggregate performance.

The current environment has been reinforced by the strong performance of large technology and artificial-intelligence-related companies. A relatively small group of market leaders has generated substantial earnings growth and market-capitalization gains, while many other companies have struggled to match those results. As a result, market breadth and index returns have increasingly diverged, making the headline performance of the S&P 500 a less representative measure of the performance of individual stocks.

Why Concentration Can Increase Market Sensitivity

Concentration creates a different risk profile from a market in which leadership is broadly distributed. If a large number of companies are outperforming, weakness in individual market leaders can potentially be absorbed by gains elsewhere. But when leadership is concentrated, a deterioration in the earnings outlook, valuations or investor sentiment surrounding the dominant winners can have a greater influence on the broader benchmark.

This does not mean that a concentrated market must immediately reverse. Dominant companies can remain dominant for extended periods when they continue to deliver superior revenue growth, margins, cash generation and returns on capital. The data instead highlight a structural vulnerability: if the relatively small group of market leaders begins to weaken while the broader universe of stocks remains unable to compensate, index-level declines could become more pronounced.

The historical comparison is also notable. The source data indicate that following the Great Financial Crisis, more than half of the largest U.S. stocks were outperforming the S&P 500 over comparable periods. The current figure near 23% therefore represents a substantial change in the breadth of long-term market leadership rather than a short-term fluctuation.

Going forward, investors and policymakers will be watching whether market leadership begins to broaden or whether the concentration trend continues. A sustained improvement in corporate earnings across sectors could gradually increase participation, while renewed weakness among major index constituents could expose how dependent the benchmark has become on a limited number of winners. For global investors, including those allocating capital from Israel, the key issue is therefore not simply whether the S&P 500 rises or falls, but how broadly that performance is being generated and whether the market’s underlying breadth can improve from its current historically narrow level.