I don't think so. For example, Fisher Tiger invading Mary Geoise and freeing many slaves all by himself doesn't make much more sense right now (and it was quite impressive already even without the God's Knights, as we already knew that the marines, including the top echelon like Sengoku and Garp, could enter the holy land).
One possibly explanation: we never saw any of the God's Knights in combat yet, even when the revos and later Kuma invaded Mary Geoise. Do they act only when the marines and the local guards are defeated?