Should You Forget the Vanguard S&P 500 ETF (VOO) and Buy the Invesco S&P 500 Equal Weight ETF (RSP) Instead?

The S&P 500’s top eight stocks account for 37.2% of the index, raising concerns about concentration and exposure if AI investment or performance falters. As of Sept. 30, the market-weighted S&P 500 outperformed the equal-weighted index over every listed period, including 15.74% vs. 11.56% over one year and 22.89% vs. 15.73% over three years. The article presents RSP as a possible partial allocation for investors concerned about concentration, while noting either approach may suit long-term investors.

Analysis

The useful distinction is between concentration risk and an AI unwind: RSP reduces the former, but is not a clean hedge against the latter. If hyperscalers trim investment, the first-order hit to NVDA/AVGO expectations could be accompanied by weaker demand for suppliers and softer earnings at companies selling into the capex cycle. Conversely, a broad capex slowdown could hurt non-tech beneficiaries too, so equal weighting does not guarantee defensive returns. In a general risk-off move, RSP’s more balanced exposure may still lag if investors favor the largest, most liquid companies.

RSP’s structural case is that its rebalancing systematically trims relative winners and adds to laggards; that can help if leadership broadens, but is a headwind while mega-cap earnings and returns keep compounding. It also embeds more exposure to smaller S&P 500 constituents and sectors outside mega-cap technology, making it a factor/sector rotation as well as a concentration decision.

Near term, the key catalyst is relative earnings breadth versus further upward revisions concentrated in NVDA, MSFT, AMZN, GOOG, META and AVGO. Over 1–3 months, monitor hyperscaler capex guidance alongside realized AI monetization and supplier demand; over 6–18 months, the thesis depends on whether returns on AI investment support continued spending. The contrarian risk: concentration may reflect earnings leadership rather than merely speculative positioning. Verify cash-flow trends and capex plans before treating a spend slowdown as established.

Key Decisions for Investors

• Do not replace VOO outright on this evidence. For a portfolio explicitly seeking less mega-cap concentration, consider a partial VOO-to-RSP reallocation; treat it as a persistent style and sector tilt, not crash protection.
• A tactical long RSP / short VOO relative-value position is a watchlist idea if earnings breadth improves and mega-cap capex expectations flatten. Size modestly: the spread can widen further if AI leaders continue to outperform. Avoid using it as a market-neutral trade without checking beta and sector exposures.
• Track quarterly capex guidance, free-cash-flow direction, AI-related revenue evidence, and breadth of earnings revisions. Falsify the broadening thesis if the largest AI-linked names continue to deliver stronger revisions while RSP persistently underperforms; reconsider the capex-risk thesis if spending remains firm and monetization evidence improves.