You may notice that Hyrule's military is rather oddly set up, with the only actual proper rank structure belonging to the Navy which is also what Zelda is most unfamiliar with. Got to remember as well, Zelda is well, literally a Princess from a medieval kingdom and while a rather large proponent of noblesse oblige is well... operating under the mindset where noblesse oblige applies.
Well, it's an organized military that isn't dependent on feudal levies, so it's not that odd. I would guess that it started as feudal levies with 'squads' drawn from a single village led by the local head man or landed knight, whom were nobility but not by any measure
rich, because they literally handled 1 village. In Hyrule's current(ly non-existent) military, that's a corporal. Multiple villages would be grouped under the baron they swore fealty to (modern day equivalent: sargeant), and the barons grouped under the count they swore fealty to (usually, although the feudal contract skipping steps wasn't unknown, because the count needs knights to serve him directly too, as did the duke and king).
Hyrule's military looks to me like a post-feudal early modern organization of the military that is very light on leadership, with the nobility still having a strong grip on the military while the military is ostensibly at least supposed to be Hyrule's/the king's. It's a sign that the kingdom successfully centralized power and broke the nobility's control of the military in favour of the king's authority, but that the nobility still plays its historically key role as the core of the nation's leadership and protectors. This is in compliance with RL history as cannon developed and the fortifications to withstand cannon became more expansive, elaborate and expensive.
The oddest things are the rank of 'knight sargeant', as 'sargeant' descends from the same root as 'servant' and no nobility would tolerate being called a servant, and the fact that apparently there were quality standards that everybody met. Quality would realistically be rather uneven and depend on local manufacturing capabilities as well as any given soldier's ability to pay for their gear. For commoners in royal service it would be expected they'd be given decent but cheap gear, but there would be considerable differences in the quality of gear for the nobility between the wealthy nobility and the poor nobility, and their ability to source replacements and repairs.