Staggered by Mechagodzilla's plasma-based missiles

As Godzilla looks up he sees a ghost from his past as a familiar metallic hiss echoes through the air. Standing before him is his old enemy...Mechagodzilla! Looking exactly as he did decades ago when Godzilla first faced him. With another hiss MG fires off a volley of missiles which connect and explode rapidly against the kaiju king. Godzilla actually staggers back wincing in pain for but a moment, but that didn't make any sense. In his current uber-form MG's weaponry shouldn't even be able to scratch him let alone hurt him. Perhaps if someone had taken the time to explain to the big G that MG's new missiles were now plasma based it would have made more sense!