Sigh...loseth said:Myths like this abound...
The experts at the time disagreed about which weapons were superior, so it certainly wasn't obvious to them, although many seemed to hold strong opinions for or against rapiers versus broad swords.
What is clear is that broad, slashing blades produced big, visible injuries, and thin, thrusting blades produced small, unimpressive injuries, which didn't seem like they should be so lethal.
The Romans used a sword, the gladius, which was short and fairly broad, but they used it primarily to thrust, because they found that slashing caused superficial injuries that were less likely to kill an opponent than a thrust to the midsection, which might not be as natural a motion and might not feel as powerful, but which is highly lethal.
The "common sense" view that a big gaping wound is much worse than a tiny hole is exactly the kind of naive view that the Romans would have mocked. Similarly, duelists learned the hard way that the tiny wounds from the "French blade" were quite lethal, even though they didn't look like much.
All this is complicated by the fact that most swords were developed for knights, who traditionally fought from horseback, where a heavy slashing sword makes much more sense than a thin thrusting blade.