Core Insights - Investors in the S&P 500 are increasingly concerned about the high concentration levels within the index, which is primarily due to its market-cap weighting methodology that disproportionately favors key holdings [1] Group 1: Market Concerns - The concentration of the S&P 500 index raises worries among investors, as it leads to significant overweighting of major stocks [1] Group 2: Investment Strategies - Some Exchange-Traded Funds (ETFs) are attempting to address these concentration issues by adopting different methodologies [1]