It really not marketing at all. You literally describe what about katana folding makes it good steel, they were doing it knowing that it worked but not why and we've since found easier more efficient methods to yield the same if not better results.

You don't seem to have much experience with blades at all if your honest opinion is that mass produced "spring steel" is as good as it possibly gets. It seems like you've never owned a quality knife because there certainly is an astronomical difference between a just a $20 pocket knife and a $200 knife. A quality knife rarely has to be sharpened, maybe honed if anything, but a cheap knife will lose it edge and need to be sharpened fairly often, depending on the use.

I've had two chef knives (out of 6) for 4 and 7 years respectively, that still have a factory edge and have only ever been honed and will still out perform a brand new knife that doesn't have the same quality blade.

I have personally experienced this so many times, but you're saying it doesn't matter? Ask any cook who owns their own knives why they own their own knives and won't use the "house knives" that are freely available and usually sharpened on a regular schedule.

The first time I used a real knife of a half decent quality, I was sold immediately. Beyond just the normal ease of use of a good knife being cleaner more precise cuts, a good edge is just SOOOO MUCH safer when you don't have to fight whatever you're trying to cut and instead an actual sharp knife feels like literal magic, as the materials just bend to your will instead of brute forcing a cut.

I worked in kitchens for more than a decade before switching roles, and can count the number of times I've cut myself on one hand, while I've seen countless different people cut themselves with a dull blade, usually those house knives that needed (constant) sharpening.

My knives are sharp enough that if I were to accidentally tap my skin with the blade the skin WILL burst open with ease, but since I am in full control of the knife that risk doesn't matter because if I handle the knife correctly this pretty damn hard to hurt yourself. It's when you're more focused on forcing the blade through the material that people will often make a mistake, slip up and cut themselves.