they definitely, definitely do.
i'm replaying right now trying to make a pure evil character with a broadsword, and it's working. only using flourishes and blocking my blade has gotten, if not very broad, extremely long and it feels slower and heavier as i use it.
most people just mash the melee button.....
i'll put it this way.. if your rush the story, only mash the melee button most of the time rather than blocking or flourishing, and upgrade your melee the first chance it's available each time, your sword will resemble the splade.