Social Capital is bleeding top investment partners. The venture firm, run by legendary investor Chamath Palihapitiya, has lost three partners  — Tony Bates, Marc Mezvinsky, and Arjun Sethi — in two weeks. Palihapitiya says the firm will shift focus away from new growth opportunities and instead be "doubling down on proven winners."   Another two partners have left Social Capital in a series of departures from the Silicon Valley venture firm.