If you are not going to add the required mats into the game to craft the legendary 600gs weapons with Weaponsmithing it means they are all going to be worthless when higher GS weapons are introduced into the game.
So either add the items required now or bump up the GS to 620 when it is available and add the mats only then.
I feel frustrated i can’t make them and even more frustrated if they are never going to be worth making and collecting those legendary items needed have been a total waste of time.