"most ... in the US" is probably going overboard, but that's not too far from the truth in LA, where, for instance, many of the restaurants in little tokyo are korean-owned, despite the namesake. there can be good korean sushi, but it mostly tends toward the cheaper end, which means it's often not as good as a japanese sushi bar, where the best sushi is exquisitely delicious (and quite expensive). it seems like japanese sushi chefs aren't interested in the lower end of the market, so cede it to others willingly, and touristy areas like little tokyo have plenty of unsuspecting customers to keep those businesses afloat.

LA has the best korean food in the US, particularly because it has the best banchan (like kimchi!). even so, i generally wouldn't go to a korean sushi restaurant for good sushi in LA.

When that's the case the kimchi is fine, though.

Here in Germany it's usually mediocre sushi and intolerable kimchi; instead if you go to a cheap sushi place you should often be ordering the pho or the bún.