It's a bit sad to say this after all the troubles the developers went through to finally make it work but i think Kubikiri is wayyy to strong now that it's finally working. It trivializes late game miniboss (Gatekeeper, Sectopods) encounters and makes some perks supposed to deal with those late game armored enemies totally useless.
Despite what you might think when first seeing it, Kubikiri is actually pretty easy to use. A good crit sniper will try to stack crit anyway and is a pretty efficient build by itself. It doesn't need to be a nest DfA sniper, i had 2 snapshoters operating with 5-6 guys GOps squads and both were built for high crit on flanked target in the early game. Later they both learned Kubikiri and their squads never had to fear Gatekeepers or Sectopods. I know it uses both actions and doesn't combine very well with Snapshot but it just meant the sharpshooter had to stay in one place for one turn when using it, not a big deal.
Crit stacking is easy if you're serious about it :
- Sniper Rifle : 10% (20 for Plasma)
- Superior Laser Sight : 15%
- Talon Rounds : 10% (they might not have the same raw damage output as other rounds but the important mod is the crit%, not the damage, they add damage by allowing crits)
- Aggression : 15-30% (enemies never come alone, you just have to kill the big one first, which was probably your plan in the first place)
- Superior Stock : 25% (obviously it won't work if you're surprised by them, good scouting is important but that far in the game you probably have enough options to scout to prepare for them)
- Get Some officer order : 20%
- Mind Merge 10-12% (20-25 with Soul Merge)
Wounded requirement isn't really an issue. Anyone with Quick Draw or some AoE attack can damage them without using up their turn.
Sure it's still a lot of requirements, but given Kubikiri's power and the fact that many of those requirements will also benefit you the rest of the time (only the stock on a snapshoter is questionable without Kubikiri) it's not really a big deal. The issue however isn't the investment/power ratio, it's really the fact that Kubikiri obliterates the usefulness of several items/perks. The Acid Grenade/Bomb is usually considered one of the useless grenades. It does however combine high shredding + rupture effect. I built one in my latest campaign as i wanted to actually see if it was really that bad and very rarely used it. Every enemy who would have justified using it was usually dead before i had to throw it, killed by a Kubikiri sniper. In squads without a Kubikiri sniper however, it proved to be a useful tool but those were few and rarely deployed in the end game where those enemies are frequent. The same could be said of Shredder rounds/perk, all of those are great tools against Sectopods, Gatekeepers and Superheavy MECS but why bother with those if you can just kill the big targets so easily. Of those 3 heavily armored enemies, only the MECs usually caused me some troubles as you can get more than 1 / guerilla mission. Multiple Sectopods/Gatekeepers might appear in long missions such as HQs, Ambushes and Golden Path but for those missions you can usually expect to use Kubikiri more than once despite it's cooldown.
I'm not someone who likes the "Nerf Hammer" much. I've complained about nerfs more than i have complained about their lack but i think Kubikiri requires some rethinking/redesign. Simply nerfing it by making 100% crit (and thus guaranteed kills) harder to achieve probably won't work. For me it would just make it useless because the drawback (half damage) is too severe for risking it when you face a target strong enough to justify using Kubikiri in the first place. I think it's terribly tricky to balance with such a drastic, almost binary, effect (you either kill the target or you more or less did nothing). It would probably be more balanced and easier to balance if it dealt 2* damage on crits (as it does against Rulers) on every enemy. It would still be strong, but not as strong. It would make Sectopods and Gatekeepers less laughable and give shredding it's rightful place (which shouldn't be to make EXO the obvious choice when ADVENT have it). It might even receive some boost to make it more useful such as increased Crit chance based on % of health lost or something more creative or lose the half damage on non crit part.
I'm not really sure as those changes would basically turn it into an improved Precision Shot but i don't really like it in it's current state. It feels like a requirement in the late game. It pushes the game even further into the vanilla "kill everything on activation" style, even the miniboss that should in theory require a lot of efforts to bring down rather than just 1 + 2 half guys (which is less than 2 guys due to the way tactical combat works in XCOM). Finally it reduces tactical diversity by being so vastly superior to other options for dealing with those miniboss.