I agree a good manager can change a lot, but 'should' is really not an appropriate expectation. City and Liverpool are miles ahead and that gap can't realisticly be closed. Then you're fighting with Chelsea, Spurs and Arsenal who are all one step ahead at this point, Chelsea arguably even two steps. A few good signings and good management bring United back into that mix for sure, but then it's still a coin toss cause you've got 4 relatively equal teams competing for 2 places from which United has the most ground to make up. Top 4 next year is possible if things turn out well, and not playing European games might work to United's advantage, but it's not by any means something that should be expected.