One of the things I've repeatedly encountered among sword enthusiasts over the years is a subtle misunderstanding that all swords of a similar design and function will handle and perform in the exact same way. There is a certain assumption that because every sword strikes along the same lines and uses the same kinds of blows for the most part that differences among similar kinds are minor. But the fact is, they have distinctions in form and design that are a result of far more than minor aspects of appearance.
Differences in typology or form --size, shape, length, weight, cross-sectional geometry, edge bevel, hilt composition-- are what establish utility. These elements are what dramatically alter how a sword can be used and how it was preferably employed. These are the factors that determine the impact damage they can cause, the penetrative force they can impart, and the manner in which they can fend off other blows. This is what defines a sword's versatility in cutting and thrusting with warding as well as transitioning between cutting and thrusting with warding. Obviously, these factors differ among different types. But they also differ among almost any two swords of very similar ones.
For example, we wouldn't look at a 12th century falchion, a 15th century Langen-messer, a 16th century sabel, a 17th century back-sword, and a 19th-century heavy saber, to then conclude that they all have the same handling characteristics. We wouldn't assume they all have the same center of gravity and center or percussion simply because they're all single-edged blades with some curvature. Their dimensions and their hilts alone, not to their mention concave or convex width, give each a unique fighting "personality". By appeasing these qualities we are able to gain an appreciation for why each was designed and how each might be best wielded.
Similarly, we wouldn't look at an early Medieval arming sword, a mid-15th century bastard sword, and a 16th century side-sword, then conclude that they are essentially all the same weapon because they are each straight and double-edged. The differences in their size, taper, and point shape result in each obviously having a different capacity to cut and thrust. What's more, their stiffness, their resilience, and their thickness of point will differentiate their puncturing capacity. Further, differences in their hilt configurations might favor certain gripping methods to facilitate some particular techniques over others.
For these same reasons we would understand that a rapier of the early 16th century variety, with it's flatter tapering blade, does not perform identically to the later acutely narrowing kind of very slender dominant in the 17th century. The former retained some cutting ability while the latter, with its thicker cross-section and thinner point, gave it up for the benefit of greater agility and speed. They each represent excellent designs of thrusting sword, but are not identical in they perform. The same can be said of the shorter and thinner "Baroque" versions that became the small-sword.
Differences among similar sword designs are hardly trivial matters of mere aesthetics or just alternative solutions for achieving the same basic performance results. The wider the variety of quality replica blades of different types you get experience with, the truer an appreciation you will find for how similar swords perform. And the more occasion you have to conduct cutting experiments with sharp versions, or just exercise vigorously with a blunt, the more you will discover about how they were effectively employed. Without such opportunity or experience it's easy to see design differences among "families" of swords as being more about stylistic or artistic choices. That sort of prejudice was a common ignorance among museum curators and antiquarian arms collectors of the recent past. Today, as martial artists and scholars of historical swords we know better and we should be able to refine our appreciation even further.
Every real sword, and in a sense, every modern-made replica as well, is a handmade object distinct and unique unto itself. Even as any given blade may fit within the pattern of well-known designs, variations in hilt composition (with differing guards, bars, handles, and pommels) can significantly alter the handling characteristics of very similar swords. Hold any two fine rapier specimens of the same style or heft any two superb katanas by the same maker and their undeniable individuality comes alive in your hand. This is why it's important to obtain good examples of many different sword types. The opportunity to compare, contrast, and learn the nuances of different blade and hilt combinations, delving into their subtleties to find which uniquely appeals to you as collector or fencer, is part of the very fascination this study offers. In a very real sense, no two swords are truly the same.