I have a theory about the different types of Usurpation soldiers. First of all, they are not wearing armor but instead have an exoskeleton that grows as they evolve. This also would explain the differences in blood and voice. Maybe it was even a natural adaption to Earth's envirement.
So my lifecycle hypothesis:
Usurpers start of by being a Minor Soldiers, they then either get fitted with external plating to become an Advanced Soldiers, resume their natural lifecycle and become a Major Soldier or get augumentations to become a Ranger. Major Soldiers then go on to become Destroyers.