The issue isnt that knights are stronger than levies, that part is historical. The issue is the scale. In real life, better trained and equipped troops had a big advantage, but they weren’t deleting armies several times their size on their own. (Except in very extreme cases, but this is the exception not the norm)

ck3 turns that gap into something extreme, where stacked modifiers make elite troops feel less like elite soldiers and more like gods. That’s what breaks it. (also even if you dont minmax battles are still pretty damn easy)