I’m not sure that is fully true - the authority on this that I think has proven out his trustworthiness in the knifemaking community, Kevin Cashen, makes a compelling argument that with correct heat treatment, pattern welding gives you the ability to mix alloys. He frequently uses an O1/L6 blend.
I am not saying that most of it isn’t cosmetic - that is certaninly the point most of the time, but, for boutique knife makers, it can give you more options if what you want is not available in a commercially made alloy. Keep in mind that most commercial steels are not the “best possible” for knives, but frequently the best balance of performance, and manufacturability (I.e. they avoid very complicated heat treats, and very expensive hard grinding with lots of embedded carbides).
I am not saying that most of it isn’t cosmetic - that is certaninly the point most of the time, but, for boutique knife makers, it can give you more options if what you want is not available in a commercially made alloy. Keep in mind that most commercial steels are not the “best possible” for knives, but frequently the best balance of performance, and manufacturability (I.e. they avoid very complicated heat treats, and very expensive hard grinding with lots of embedded carbides).