I feel like either I'm misunderstanding something about how the game works, or the Balanced Blade weapon is drastically underpowered.
From what I gather, every crit damage/critical effectiveness modifier in the game is effectively a damage multiplicator on the critical hits (there isn't anything that just adds an independent amount of flat damage at any point in the calculation). That generally isn't an issue, since most effects that improve either are just buffs to the character as a whole (so everything you do that crits gets that boost). This includes the only other weapon that boosts the damage of criticals in any form, the Chrysanthemum Petal, which adds a +50 to critical effectiveness (so it significantly increases the effectiveness of criticals for your other weapon if you're dual-wielding, alongside boosting any non-weapon crits).
That isn't the case for the Balanced Blade. It, instead, deals 15% more damage with its own critical hits.
I'm not against that idea. It plays into the fantasy of a high-damage crit build that you might want to go for with a thief class. The problem comes after you crunch the numbers (which I'll freely admit I only did after I equipped the Fan of Blades power and noticed it was apparently dealing a bit more damage than Deadly Shadow against targets that aren't crit immune). When you do, you realize 15% is just way too little to make a difference.
The Balanced Blade simply doesn't have the base stats to make itself functional. It will always be underwhelming, damage-wise, compared to the competition - and it doesn't really make up for it with its other stats. It has a +10 to critical and accuracy, and is a melee weapon. This makes it, in the best case scenario - or, in other words, if you're critting basically every attack (which you can approach with the right set of equipment and skills, thanks Zo!), it's still overall worse than the dagger thieves start the game with. Sure, it has 15 accuracy over it, but for that you're losing the thrown tag, 10 armor pen, 5 evasion and (worse of all) damage.
Yeah, the dagger crits actually just do more damage, even ignoring armor penetration. That's because it has 5 base damage on the Balanced Blade, and that's a big difference. How big? Well, over 15%, as you can see in this calculation: 30*1.15=34.5. So the Balanced Blade always deals a bit less damage, and that's accounting for a 100% crit chance, which you probably won't have, ignoring the drawback that is the existence of crit immune targets, and taking armor out of the equation (while, to be fair, also discarding accuracy).
I do think that the balanced blade should deal less damage than the alternatives when you don't crit. I do think its base stats should be worse overall than the dagger, so that the effect has a tradeoff to it. But, as it's implemented in the game, you take the negative but don't get to an actual upside when critting. It probably should have a larger damage multiplier than 15% (gut instinct says 30% would be fine, but I'm not involved on the dev side of game balancing), so that it still needs crits to shine but actually does get to shine when you crit. Failing that, it could get a small base attack buff that brings it closer to the power curve of other weapons (raising it to 32 or 33 damage, for example).
It could even take a base damage nerf, if it came paired with a suitably large boost when critting. If it had something like 25 base damage, but crits with it gained a 60% damage bonus, for example, then it would be as if it had 40 damage as its base value when critting, which is outstanding, at the price of being way, way weaker than any comparable weapon when not critting,
This is bothering me because I find the idea of a weapon that rewards building around crit chance actually really cool, but the balanced blade, while having an effect that implies it does that, actually just punishes not critting instead, with no meaningful upside even when you crit.
