A closer look at brokerage holdings reveals how the S&P 500's composition has shifted considerably. Technology stocks made up close to 40% of the Vanguard S&P 500 ETF by mid-2026, according to VanEck's "S&P 500 Concentration Risk," and the top 10 holdings controlled close to 40% of the full index. Analysts at VanEck and Royce Investment Partners have pointed to small-cap and international ETFs as segments that sit outside the cap-weighted S&P 500's concentration profile. The case starts with understanding exactly how lopsided the S&P 500 has become and why recent analyses flag the tilt as urgent. Lee concluded that a passive S&P 500 allocation now functions as an unintentional active sector bet, whether the investor planned it or not.