West Ham’s co-owner discusses regrets over Slaven Bilic, why it may be time to stop allowing the manager to choose all the main transfer targets and how his sons could take over from him “I feel like I haven’t done well enough,” David Sullivan says as he considers how swiftly and brutally West Ham United’s grand ambitions have unravelled after 18 troubled months in their huge new stadium. “Nobody’s done well enough. I work my…