There are a number of reasons why I believe that mainland Eurasian swords were considerably more developed in both form and usage than the Japanese sword. I mentioned the European swords because those are what I'm more familiar with versus say, Persian, Chinese, Middle Eastern and Indian forms.
Taken from a macroevolutionary scale, one of the worst things that happened to many Asian societies is that they were culturally conservative and had the geographic and societal wherewithal to close themselves off from the greater world. Removed from the need to constantly adapt to innovation, they stagnated.
As mentioned in a previous post, 15th/16th century katana combat more or less resembles contemporary European longsword (2 handed sword) combat. As Europeans expanded their reach, they ran into differing styles of combat (both personal and massed), their styles changed to reflect the realities of fighting. European sword combat developed along multiple parallel lines that clearly differentiate between the circumstances in which you might be expected to use a blade in anger. OTOH, the Japanese never contended with that. They stuck with what they knew was effective against each other.
This is most clearly demonstrated in an examination of the evolution in the types of swords that Europeans developed in a few hundred years, from long swords to rapiers to smallswords to broadswords to backswords to sabers to zweihanders to cutlasses to spadroons and every thing in-between.
While there are differences between the light Yagyu Shinkage ryu blade and a heavier Katori Shinto ryu blade, these are variations of one thing - a relatively heavy, short, single edged cutting blade. OTOH, on a single Napoleonic battlefield, you will see a dozen variations of swords specialized for the cut versus thrust, depending on the function and the philosophy of the varying warring parties.
Amongst people who actually used swords against someone who was trying to kill them, there is no argument - European sword designs and subsequent fighting methods had a much larger breadth and depth of exposure.