美国股市目前的估值约为标普500指数预期盈利的22倍，虽然高于历史平均水平，但仍远低于1990年代末或2020年的泡沫时期。作者认为这并非泡沫，因为市场由一批极具创新力和盈利能力的企业所驱动，股价并未脱离合理的基本面价值，不同于1920年代或1990年代网路泡沫时期的盲目狂热。

标普500指数未来的成长高度依赖少数公司的表现。预计仅13家公司将贡献未来四年标普500营收成长的一半，远少于前五年的水准。这些公司主要包括「七巨头」（扣除特斯拉）、人工智慧相关企业如博通、美光、甲骨文和戴尔，以及福特、沃尔玛和麦克森等。同时，利润率已从1990年代初的4%飙升至15%，进一步扩张的空间有限，因此营收成长成为推动盈利增长的关键。

市场集中度的风险已在2026年初显现：剔除七巨头后，标普500年初至今上涨约13%，优于含七巨头的整体指数表现约3个百分点，而七巨头自身仅录得约3%的涨幅。作者总结认为，标普500的问题并非估值过高得离谱，而是持续成长的命运掌握在越来越少的公司手中，一旦这些公司令人失望，市场的高速增长时代可能就此终结。

The US stock market is not in a bubble, according to the author, because its valuation of roughly 22 times forward earnings for the S&P 500 is driven by highly innovative and profitable companies rather than irrational speculation. While the premium is higher than usual, it remains well below the extremes seen in the late 1990s dot-com era or even in 2020, and the underlying businesses represent some of the most impactful enterprises in history.

Future growth for the S&P 500 increasingly depends on a narrow group of companies. Just 13 firms are projected to generate half of the index's revenue growth over the next four years, down sharply from the previous period. These include most of the Magnificent Seven (excluding Tesla), AI-focused companies like Broadcom, Micron, Oracle, and Dell, along with Ford, Walmart, and McKesson. Meanwhile, profit margins have already surged from 4% to 15% since the early 1990s, leaving limited room for further expansion and placing the burden squarely on revenue growth.

The risks of market concentration are already visible in 2026: the S&P 500 excluding the Magnificent Seven has gained about 13% year-to-date, outperforming the full index by roughly 3 percentage points, while the Magnificent Seven themselves have managed only a 3% return. The author concludes that the core concern is not that the S&P 500 is dangerously overvalued, but that its continued growth rests on an ever-shrinking set of companies—if they fall short of lofty expectations, the market's era of rapid gains could come to an end.