You do understand that a vanguard in plasma/high energy cell has exactly the same defenses and damage reduction as a commando?
Its a fairly understandable misconception that some commandos have, because when you *face* a vanguard 1v1, they'll usually win, with quite a bit of their health left.
The reason of course is not extra mitigation/defenses, but because the majority of THEIR damage is instant, and not effected by your attacks - whereas commandos, particularly gunnery but also assault to a lesser extent lose damage output under fire.
Assault vanguards also have a very high proportion of damage that bypasses armour. Assault 'mandos can't spam ion pulse, and gunnery mando's aren't even in the same ballpark.