You would never enter a battle with a dagger in hand because it's a side-arm, but that doesn't mean you wouldn't employ it in battle. Especially in later periods where plate armour started to be used, a dagger was an effective sidearm to have because given its size and length it was very efficient and accurate at getting between the plates of the armour and dealing a lethal wound to your adversary (in close quarters and once the other knight was disabled, that is). This is my understanding anyhow, and I don't see why it would be so incongruent with the world of Eora too.
Indeed. A lot of historical fencing manuals depict two armoured fighters, armed with daggers, grappling with each other whilst standing up. The manuals describe various methods of locking down your opponent's weapon and bringing yours to bear against their weak points (usually the face).
That said, the daggers used for this sort of fighting are really better represented by stilettos than daggers in Pillars (things like rondel daggers).
Actually if anything the dagger makes sense as a major weapon in Eternity. With the advent of firearms (not to mention the cross bow) heavy armor because largely pointless, because those weapons could punch right through it. Thus people started wearing lighter more mobile armor, and when in melee started using lighter more flexible weapons. Like the Rapier, Sabre, or "Side" Sword.
Crossbows really couldn't punch right through plate, particularly not the case hardened plate that was used in the period that is equivalent to Pillars setting.
Yes, they had enormous draw weights (as high as 1200lbs) but they had tiny draw lengths compared to longbows, and crossbow bolts were a lot lighter than longbow arrows (they lose velocity to wind resistance faster). These differences lead to surprisingly a similar performance from the two weapons at normal ranges.
This doesn't mean that crossbows couldn't put men-at-arms out of action, they certainly could, but much like longbows they relied on hitting weak points in the armour (most often an exposed face, but also some gaps in joints or thinner pieces of armour) to do so, together with a very high volume of fire to make this likely. Also, obviously against mounted men-at-arms horses were generally more vulnerable.
By the way, the sabres and rapiers that were used in battle weighed about the same (sometimes more) than a typical arming sword. Their modern day fencing namesakes are far lighter.
My understanding is that in Renaissance times plate was still pretty damn effective against firearms (though eventually it would grow obsolete), and also crossbows, and was thus commonly used up until the late 17th century ('commonly' for those who could afford it, that is). Also 'heavy' armour wasn't really that cumbersome - there's plenty of tests on YouTube that you can see of people in full plate showing off just how flexible full plate was, even being able to *swim* in full gear. The weight may seem scary at first but it's distributed through your whole body, thus making it relatively much lighter than when simply lifting it (of course you would only really use such armour for an actual battle, and not for travelling or the likes the way characters in an RPG do). Games ignore just how effective armour was usually - even a thick enough gambeson could provide excellent protection against arrows, slashes and the likes. Also my understanding is that sabres are pretty top-heavy weapons and thus not very nimble, whereas rapiers used to be very heavy, on average heavier than arming swords even. The change that came with the implementation of full plate was especially with regards to a new focus on piercing: slashing against plate was pretty useless, so swords were adapted to best be able to reach and pierce the "weak spots" in the armour, these being the parts that were not covered (slits, joints and the likes).
Indeed. There's this idea that armour was useless against the weapons of the time, but it's demonstrably false. Tests done with good quality reproduction plate show longbow arrows could, at best, penetrate to about an inch depth i.e. not enough to injure (there's a thick gambeson on underneath that plate). Breastplates from the seventeenth century were tested against musket shots to prove to their buyer that they'd provide protection. People in the past weren't idiots, they wouldn't have loaded themselves up with a heavy suit of armour if it didn't work. Armour worked.