Am not gunna lie the author really dropped the ball after idk.. chapter 2? This whole manga makes little to no sense.As strong as some of these knights are, they basically are tactical nukes. That's probably where the Kingdom's power projection comes from. The complete reliance on these super powered knights has also left other aspects of the Kingdom's forces to be little more than set-dressing, when they exist at all. Sort of like the police in Gotham.
Or maybe we're all putting more thought into this than the author did. ¯\(ツ)/¯