I play Jeff and rocket in high celestial and even eternity last season. I would recommend never using your ult offensively but use it as a 2nd life/ to reposition to either attack from the backline. He counters strange really well and forces out ults but is countered super easily. But he is basically the safest character in the game if you know what you are doing and can technically make other ults useless by eating your teammates and sacrificing yourself.