It seems to me that sword designs were ethnically oriented--functionality as a second priority. Perhaps a misconception and of course, different eras, but the West Asia seemed to love scimitars, Japanese are known for the thick katana, while bendable longswords are known from Europe. Wouldn't a certain design and techniques (such as smelting techniques) ultimately supersede all other factors or are swords just not as devastating as guns therefore certain aspects can be overlooked? How did metallurgy evolve across the lands?
Weapons are developed to face enemies in one particular area in one particular time.
For example, the European longsword was designed to fight the most likely enemy you'd find in the region - either unarmoured opponents in a self-defense situation, or armoured opponents on a battlefield. It can both cut and thrust, and its relatively large quillons (compared to Chinese and Japanese swords, anyway) is very useful in a sword-to-sword bind. All of which is effective in unarmoured fighting. In armoured combat, the quillons can be used to hook the opponent, the pommel can be used to... Well, pummel the opponent, and by half-swording, you effectively gain a short, stiff point that can be used like a short spear. All these features are useful in a situation where both you and your opponents are heavily armoured, and close grappling is more often than not the deciding factor in a fight.
So as you can see, form IS function when talking about swords, and every sword is designed to be functional IN ITS SPECIFIC CONTEXT, that is, fighting the opponent one is most likely to encounter in that specific time and place.
Edit: to illustrate my point on medieval European fighting, here is a video of historical armoured combat techniques