>>> "That system is a hold-over from the origins of modern military structure in Europe’s early-modern gunpowder armies: the commissioned officers (whose commission, to be clear, came from the king) were drawn from the aristocracy and often the nobility, while their non-comissioned subordinates were drawn from the common soldiery who were in turn recruited from the peasantry."

Yes, it is fun to map social structure onto armies and then be all judgmental about the inequality. Or you can study the actual practicalities of war. Top of the list: Officers need to be able to communicate with people at a distance. They need to be able to read. Until very very recently that meant they had to be from the upper classes.

Soldiers in the past also didn't do "basic training" as we know it today. If you want a soldier to obey orders then those orders better come from someone who held some sort of prior authority over the solider. Military discipline requires structure. When turning farmers into soldiers the only way to keep them in line is to utilize an existing structure, ie social class. Farmers (the bulk of soldiers) will obey orders from their landlords. They won't obey some random person just because some other random person tells them to.

Just after the soviet revolution the Russian army toyed with setting aside social class, even attempting democratically-elected officers. It did not go well. They quickly reverted to the old system.