E-utopia, you need to remember that Western history was not always one of people wielding huge can openners. The period when plate armor prevailed was really only a relatively short period, say later 13th through the 15th Centuries. Before that, you had mail and evolving plate and after, you had guns ending the effectiveness of armor. The gladius of the Romans, while hideously effective as a slicer, was primarily a stabbing weapon for use against unarmored opponents or those who were, at most, armored with mail. The point would very effectively split open the rings in any mail. The gladius grew into the spatha, a longer sword that could be used from a horse for slashing, but was still light and nimble. This was the basis for the European sword of the Dark Ages, up until the Vikings. Unskilled swordsmiths of the period led to increased weight, as they were less able to do the finer work that had been done in the Roman fabricae.
The Vikings revolutionized swords by introducing the fuller (no relation) or blood-groove (sic) which added strength but lightened the blade. Viking blades were famous for their quickness and lightness, even as slashing swords. This was the basic Western style sword, as evolved by the Normans (evolved Vikings) until it became necessary to start openning cans and the swords became heavier.
With the introduction of handguns, any peasant could take out an armored knight, so armor began to be phased out as both excessively heavy and expensive. As armor was being phased out, swords became lighter and thinner, arriving eventually at the rapier style. a pure thrusting weapon, in the manner of "The Three Musketeers". These swords were truly deadly in skilled hands. The final evolution of this was, I suppose, the smallsword, a light and deadly item with a blade about 30"-33" and weighing in at just about one pound or less. Examples of these may be seen in the dress swords worn by such as George Washington, but, while male jewelry, they were deadly jewelry in skilled hands.
BTW, the daimyo in Japan took note of the effect of handguns when the Europeans first introduced them and effectively banned them during the Tokugawa Shogunate onward until Peary and his "Black Ships" appeared off Japan's coast in the 1840s.
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Walk in the Light,
Hugh Fuller
