As of the last five years or so for Korea and probably a bit longer for Japan, I feel like both countries have put in place a steady production line of decent-ish players coming out of the youth levels. A lot of them stay in Asia because it's not worth it to leave the comforts of home to sit on the bench, but most of the NT-level players could do a job for lower-tier squads in Europe. Not relying on one-off outliers like Park and Son to carry a bunch of dross anymore.
Son is basically a shell of himself this WC and we look about as good as we have in the last decade or so. Results just aren't going our way.