Today’s market landscape is defined by extremes that challenge conventional portfolio construction. A small group of mega-cap stocks now represents an unprecedented share of index weight, profit generation, and capital spending, raising important questions about valuation, diversification, and risk concentration. With this in mind, it was great to have Andrew Lapthorne, Global Head of Quantitative Research at Société Générale, back on the Alpha Exchange. Drawing on long-run valuation distributions and profitability data, Andrew examines whether today’s market qualifies as a valuation bubble, not through narratives, but through measurable historical comparisons. His analysis highlights that while headline index multiples appear defensible due to strong profits among a narrow group of companies, the average stock is more expensive than during prior bubble periods, including the late-1990s technology cycle. Our discussion also examines how passive investing and benchmark constraints...