Honestly the ruby knife is overpowered because it's basic ability is basically a double strike. All other abilities are garbage with the exception of the last one which does slightly less dmg but causes bleed.
I like to craft any item once to fill my crafting list

Just because I enjoy the crafting aspect. But to be honest I think you could argue that you can use the knife for rest of the game. Some late game weapons may be slightly better though.
I guess I am a "bad gamer" because I mostly play Katalist for the atmosphere, story, sidequests, quests and the scenes. I do not really care about the admittingly very challenging combat. I usually play on the lowest or second lowest difficulty.
I think it's kinda funny to get stressed out or even ask people for help just because you refuse to lower the difficulty for 1 fight

Either you got that urge to challenge yourself or you don't. Asking for a "guide" is kinda silly because you can just lower the difficulty and I guess a majority of players here play it on the lower difficulties.
You may get less exp but you can finish the early bosses in 2 or 3 rounds. Also on high difficulty it takes HOURS to get enough materials to do all the crafting.