Wall Street rebound driven by smallest number of stocks on record

The FT article (paywalled) says a recent Wall Street rebound in the S&P 500 has been driven by the smallest number of stocks on record. That narrow leadership means headline index gains may overstate market health, increasing risk of a pullback if the few top performers falter. The market impact is that breadth-driven caution could prompt rotation, weigh on small- and mid-cap performance, and leave the broader market vulnerable despite index-level strength. Investors may respond by trimming concentration risk or waiting for broader participation before adding exposure.