Take your first example: If momentum campaigned against the leadership, presumably they would do so because bringing down the leadership is a good thing. There would be no hypocrisy if momentum didn't disband its own leadership, since it presumably doesn't suffer the same faults.
When they campaign for democratising the party, they do so because apparently democracy is a good thing of which the part should have more of. It is hypocritical to deny their own members the very same good thing that they want more of for the party. Why, are their members not deserving of democracy?