“I am big,” Norma Desmond insists in Sunset Boulevard. “It’s the pictures that got small.”On Wall Street just the opposite has been taking place. The business has gotten so big that it has made the stars seem inconsequential. That’s one reason it has become fashionable of late to lament the decline in talent, as evidenced by the lack of succession planning for hastily departed chief executives at Merrill Lynch and Citigroup and the strained searches for replacements that followed. Merrill, of course, selected New York Stock Exchange CEO John Thain; Citi in early December named investment banking head...