You’ve asked a lot of questions and covered various topics, so I’ll stick to the main ones.
Giants abound in the folklore of the British Isles and Ireland, and Cornwall has a lot of legends about giants. Some are good, some are bad and some are ambiguous. What is noteworthy is that they are very often associated with large, imposing geological features. There’s also a founding myth in Cornwall that involves the slaying of a giant. It’s difficult to know how much of this is ancient lore and how much is medieval fantasy, because giant stories are found the world over. What I think they may represent, and it’s just my personal view, is that we are dealing with ideas of overcoming the primordial forces of the land. They are human-centred myths with human beings usually triumphing, through astuteness, over forces that are much more powerful than them.
Now, this might not be to everyone’s liking, but dragons don’t get a good press in Celtic myth and folklore. Dragons aren’t good at all, and they usually symbolise strife, lack of fecundity and so on. They also don’t seem to feature much at all in Iron Age Celtic iconography, serpents – especially ram-headed ones do, but dragons don’t show up at all if I’m not mistaken. Later, in the medieval materials we find dragons, but they’re not the modern friendly, wise dragons of popular fantasy at all. So, I think the jury’s out on dragons. Again, I think that what they symbolise is the chthonic, chaotic and primordial forces of nature that would have been very frightening to earlier peoples and not without good reason given some of the harsh realities they had to live with on a daily basis. When it comes to dragons, however, I’ll not exclude the remote possibility that some prehistoric creature may have survived somewhere or other and this vague memory got passed down in legend.
It’s interesting, because swords were considered magic and special in many traditional beliefs from around the world, almost imbued with their own souls, so to speak. What I do think is interesting is if you think about ancient Bronze Age smithing, you have a crucible or cauldron over a fire, you use air to increase the heat, you use this crucible to smelt the ores/bronze, a rod or ingot of bronze as a raw material, a stone mould in which to cast the bronze and water in which to temper it (?), so you’re making something with earth, air, fire and water and when the sword is ready in the mould, you literally draw the sword from the stone. There’s food for thought in that.