While a general consensus for the replayability or campaign length of Vanquish is that It's Short, So It Sucks! (you can complete a playthrough for around 4-6 hours on Normal difficulty), a lot may seem to forget the mission briefing given by Burns in the prologue. Your squadron is given an approximate of 8 hours to complete the operation before "New York becomes the next San Francisco". When that is taken into consideration, the game's short campaign length makes a lot more sense.
The humanoid giant form of the Argus has weak spots on its limb joints, such as elbows and knees. This also holds true for the real-life suits of armor worn during the Medieval era; leaving the joints unarmored prevents stiff movements and allows flexibility in combat, but those would expose vulnerability as a side effect.