1. Dead history is irrelevant. Weapons were canonically first made by Arachne. Considering how major a development it was, I highly doubt it would be forgotten if someone else made a Weapon first.
2. It being a wizard blacksmith is irrelevant. Once again, Arachne was the first person to fuse people with weapons. Your app has Kage Ryu predate that, and as such, massively violates canon.
3. It isn't the weight that's a issue, it's the fact that said weapon would be really unweildly to use.
4. Ragnarok is a demon weapon when we first meet him, and has/is black blood. That means he's going to look pretty fucked up. Excalibur, meanwhile, is a holy sword, and was who Arachne was attempting to emulate when she first made weapons. Both are major exceptions to the rule.
5. What dragons are known for is irrelevant. Weapons cannot use magic. Giriko is never stated as using magic to do the transfer, as far as I'm aware, and his golemcrafting skills is explicitly stated to not be magic.