The reason Mycroft seems to see and know everything is that he has little psychic flashes of things that are going to happen. Taking a job that gives him control over CCTV and intelligence gathering is actually a convenient cover for knowing all the things he shouldn't know. He taught Sherlock the art of deduction so he'd have a cover if he developed abilities too, but he never did, and a wedge was driven between them because Sherlock knew he was keeping secrets but Mycroft was afraid that if Sherlock learned the truth he'd start doing experiments on himself to try and activate his powers.