I started the game with a basic Sword/Spear build since I was unsure how I would want to go through, and leveling Health/Ki/Spirit is kinda like the "default" build. It's definitely a solid setup, but it got kind of stale so I figured I'd switch to a build using the weapons I found the most interesting, Dual Swords + Kusarigama, and use some Ninjutsu. And I like that as well, but once I started filling out my skill trees and actually using the weapons, I came to feel like the Dual Swords are just so utterly simplistic. Don't get me wrong, I think they're pretty good. Not as good as the single Sword and not as good as the Kusarigama, but I think they're actually better all-around than the Axe and about as good as the Spear – just way more basic.
So I took a look at the Skill Trees and Skill Customization pages to try and see if my feeling was justified, and I feel like it is. I'll start with the number of Customization slots there are, since this is the most direct influence on the versatility of your gameplay experience with a weapon:
|Weapon||Universal Slots||High Slots||Mid Slots||Low Slots||Total Slots|
So, right off the bat, we can see the Dual Swords have the least Skill Customization slots. However, this number is actually misleading/flat out wrong. The reason for this is that one of each of the Dual Swords' High, Mid, and Low stance slots are R1+O, which can only be filled by Sign of the Cross, meaning it should be a Universal skill (like the Kusarigama's is, even though Kusarigama has 3 skills it can assign to R1+O). If we make that change, the Customization slots look like this:
|Weapon||Universal Slots||High Slots||Mid Slots||Low Slots||Total Slots|
Now the Dual Swords only have 10 slots available! And look at Low Stance – only one Skill slot. And you can feel this in-game. The Low Stance on the Dual Swords feels so pitiful, since you can basically only auto-attack, guard, and dodge. There's nothing you can do while guarding, nothing you can do after heavy attack combos, and only one combo finisher after light attacks (and this combo finisher is shared with the Mid stance!). The High Stance also feels pretty weak, because it is. The only thing you can do with the High Stance aside from auto/roll/guard is Whirlwind or Water Sword, depending on what you assign (I have no idea why one of those wasn't assigned to guard+light instead of guard+heavy), and do the one leap strike finisher after your light attacks. The High Stance is maybe a little more forgivable, since the High Stance is usually the simplest stance, but it still feels noticeably restricted compared to other High Stances. The Mid Stance is the only redeeming quality of the Dual Swords, since it actually does have a fair amount of slots available and also makes good use of them. The Mid Stance feels pretty good on the Dual Swords, and is actually very powerful. However, it also has some issues with having enough options to put into those slots. Which brings me to the next point: the number of unique Skill nodes in the Skill Tree itself.
The Dual Swords are also lacking in this category, with the result that not only do they barely have any Customization slots, almost all of them have only one option. The only ones that have two options are High – guard+heavy and Mid – guard+heavy, guard+light. None of the slots have three or more options. If we examine the actual number of Dual Swords-unique Skill nodes (i.e., not including things like Grapple, Flux, Living Water, etc.), we can see exactly why:
|Weapon||Unique Active Skills||Active Upgrades (% of Total Active Nodes)||Unique Passive Skills||Total|
|Dual Swords||12||6 (33%)||2||20|
From this, we can see that the Dual Swords are only one node off having the least total, and just as importantly, they have by far the highest % of their total "Active" nodes relegated to upgrades (meaning, essentially, they are actually "Passive" nodes). Obviously, these two things come together to mean the Dual Swords have definitively the lowest number of unique Active Skills they can utilize. When you add in the fact that Water Sword I and II are mostly useless since they're nearly 100% inferior to Whirlwind I and II, and the fact that the Mid Stance's skills that share guard+heavy are basically the exact same skills as the two that share guard+light, the Dual Swords get knocked down to pretty much just 9 useful and unique Active Skills. Compare that to something like the Kusarigama or Spear, which have 17/18 Active Skills respectively, all of which can be useful in the right situation and none of which are barely-altered copies of other skills on the same weapon. Obviously these are the most versatile weapons, but the Dual Swords hardly even have access to half of what they do, let alone what the they are able to utilize simultaneously in combat. The Sword and the Axe also have access to ~50% more useful/unique Skills, and also both have multiple more Customization slots.
Overall, it just baffles me how little Team Ninja gave to the Dual Swords. The Axe is a little light on total Skill nodes as well, but has much more useful and varied Active Skills in general as well as having roughly a third more Customization slots. And compared to the Sword, Spear, and Kusarigama, the Dual Swords feel like a child's toy in terms of simplicity. And it just doesn't make sense. Realistically, the Dual Swords are probably second only to the Kusarigama in terms of complexity in "real life." You would think that this would translate to having more Active Skills and Skill Customization slots, the way it does for the Kusarigama. And they obviously put a lot of work into the basic moveset of the Dual Swords. It's the most intricate in the game, even including the Kusarigama. But then they just decided to give up after that, or what? Even if the Dual Swords just got some "translated" versions of Sword Skills they'd be drastically better than they are now. But I really think something needs to be done. I'm not optimistic, but I'm hoping that maybe timed simultaneously with the release of DLCs and new weapons Team Ninja might patch in a handful of new skills, because at this point I just feel sad whenever I use them.
TL;DR – Dual Swords have the lowest number of unique Active Skills in the game. Not only that, a handful of the few Active Skills they do have compete (pathetically) for Customization slots taken by other skills, leading to the Dual Swords also having the lowest number of Customization slots usable (and thus the lowest number of Skills usable "simultaneously" in combat). Overall, this is extremely noticeable in-game, with the Dual Swords feeling like by far the most limited weapon type. They probably won't, but hopefully Team Ninja gives them some love in upcoming patches (maybe alongside major content drops like DLCs/new weapons).
EDIT – For the people pointing out that the Dual Swords are, in fact, strong, and that their base moveset + God of Wind is fantastic – I agree. I mentioned I think they're at least as powerful as the Spear and Axe, and the balance of power is good enough that I don't think even the Kusarigama or single Sword are that much stronger. I'm not saying the Dual Swords are under-powered, I just think they need some more skills so that they have some diversity and not every single encounter for every single player goes exactly the same.