From the research I did the japanese steel knives have a much higher hardness rating and maintain their edge sharper and much longer if you don’t do anything stupid with them, like drop them on the edge or cut into bine by accident.
German steel knives have a marginally less sharp edge (but still super sharp) but is far more resilient when it comes to not chipping as they are less brittle.
Part of it comes from the fact that traditionally Japanese knives aren’t massively used for cutting into animals with thick hard bone structures, and traditionally you slice rather than chop into common meats used in Japan.
This is also seen in the fact that traditional Japanese santoku knives tend not to taper (because they aren’t used to rock chop) and they don’t form to a point. That’s because basically while you can tap chop with it, that’s mostly intended for vegetables and meat is sliced in a drawing motion.
A western chefs knife though does taper and is thicker at the back, because it’s an all round knife that is intended be used for tap chopping, rock chopping, slicing, as well as chopping through meat joints in a pinch.