on the contrary. Investment bankers make big bucks based on bonuses and long hours, not on their ability to beat the market.
Due to the nature of the IB job, there is a distinct China wall between IB and trading of stocks; most investment bankers do not trade stocks. The info that they have on hand, can tantamount to insider trading if they were to trade. The level of compliance these days, and the work load - dissuades investment bankers from trading.
In short, they don't have time to trade lah