When it comes to considering swords, what we are dealing with, really, are objects that are no longer commonplace necessities. Thus, practical experience with them is simply rare. While we understand the science behind first working iron into steel and then into long fighting blades, there are many aspects to swords that are not yet well appreciated. A major part of what I try to do in my research and teachings is to convey some of this. For instance, consider how not all swords were built for the same physique and same conditions of fighting. Obviously, not all were intended to face the same kinds of armors or target materials. There are large swords, both replica and historical, that to me just don't think "feel" right. But I can tell that in someone else's hands they would be effective. The matter is, real swords cannot be properly evaluated inside a museum storeroom by merely standing there holding them wearing street clothes and modern shoes. They were meant to hefted; to be moved adeptly by adroit hands using energy and speed.
I own several modern replica swords that almost feel awful --that is, right up until you put on some armor and it changes their center of gravity completely whereby they suddenly are eminently wieldable. I'm sure the same must have been true with how many historical specimens. Then there are smallish-swords which I've handled that I thought were too dainty and effeminate for my taste and fighting style, yet they were real authentic specimens amazingly constructed. They weren't made for the exigencies of chaotic battlefields but they are no less elegant and deadly tools superbly conceived. There are ones that really work best when you are on horseback, where the angle of strikes are much more limited, there's no ability to employ agile footwork or use many close-in actions. The weapon might feel "wrong" somehow to those unfamiliar with the dynamics of riding...until you're mounted, then it feels pretty sweet.
How different kinds of swords and weapons were genuinely used, and how fighting men trained with them, is a subject of deep investigation. How exactly so many assorted designs came about and even how they were constructed, is a matter of considerable study as well. We simply don't know everything we wish we did. Nonetheless, we do know the dimensions of countless different kinds of swords and why they have the blade shapes they do. The same goes for the true weights and cross-sectional geometry of all manner of swords. The metallurgy may in certain instance still be something of a mystery, as is the exact manner they were crafted, but the rest is largely known. It's attention to these very factors which today produces light, agile, and effective reproduction weapons capable of doing all the techniques and actions we find in the many fight-book sources available for study.
Without context, it's very easy to misunderstand why a particular type of sword feels so different from another style. It's possible to attribute erroneous qualities to them and mistake why a particular ones doesn't "seem to work" the way you expect. This is because it's easy to forget that swords are just man-made tools devised for specialized action in skilled hands. Swords simply have to strike, to slash or stab or perhaps both, and do so without warping or snapping under those pressures. Consider also that sword blades have to absorb shock. They have to withstand the forces not just from the constant violent impacts they deliver with edge and point (and hilt) on resistant targets but also shocks from continuously warding off oncoming blows and forcibly clashing up against other weapons. (There are ideal ways to do this...and then there others much less optimal).
As a result of all this, swords suffer a certain amount of trauma over time. Edges and points wear down, while blades warp and crack. It's inevitable. They wear down from proper use and they break down from improper abuse. No matter how well made they are still perishable tools subject to the laws of physics. They not indestructible objects. They are not imbued with supernatural forces. There's no fantastical properties involved. Much as we might imagine otherwise, there are no "magic swords."
