At first glance, the decision by veteran activist Nelson Peltz to take a 5.1% stake in Lazard looks like a vote of confidence in the 160-year-old firm.

Last week, Peltz talked glowingly about how the balance of power on Wall Street is shifting away from the "impaired brands" of bulge-bracket investment banks to independent advisory firms, and of how Ken Jacobs has made enormous progress since taking over as chief executive of Lazard after the death of Bruce Wasserstein in 2009.