The Russell 2000 Index, a benchmark for US small-cap stocks, has surged 20% year-to-date, marking its strongest performance since 2003. In contrast, the S&P 500 Index has gained 10%, while major tech stocks, known as the "Magnificent Seven," have increased by less than 3%. Analysts caution that the rally in small and mid-cap stocks is primarily driven by unprofitable companies, raising concerns about excessive optimism and potential bubble risks.