Hi, welcome to the forum! We lurk a lot, but that doesn't mean there's noone here. I'll see if I can answer your questions.
in general, is there a difference between blunt and bladed weapons? Is there some hidden difference, like blunt weapons are stronger vs. armour?
In the game code, there are different damage types for different weapons - i.e. slashing, piercing, blunt, etc. HOWEVER, last time I checked this had no bearing on game play - it is a leftover from earlier development that was either never fleshed out or was phased out for other reasons. As a result, the current game does not distinguish between, for example, being a spear and a warhammer, beyond the actual damage dealt.
do light weapon always swing faster compared to heavy weapons, or heavy weapons are just better if you can wield them well. On top of that, does light weapons accuracy max out as well? Meaning there's no difference in the late game, making lighter weapons obsolete
This one's a bit harder to answer. I suppose that, theoretically, there is a cap in how quickly you can swing your weapon - time is discrete, after all. (That's physics for "there is some base indivisible unit of time," i.e., you can't ever have half of a "time unit" whatever that time unit is.) I'm not sure how fast you would have to be swinging to hit that limit in IVAN though; I'm not sure how small IVAN time units get. Once again, there is a HOWEVER: You'll probably never get there. With artificial limbs you might be lucky enough to get into the low hundreds of Dex, and using only one weapon type all game might cap out your skill with that weapon, but you probably need more than 1000 Dex to actually hit the time cap.
As for accuracy: Please someone correct me, but I want to say that there is a maximum "accuracy" for a weapon. But high dexterity will still help you here: accurate weapons wielded by dexterous characters tend to hit limbs more often. Arms and legs are a lot easier to remove than torsos and groins, and as an added bonus even Ur-Kahn can't do a whole lot if he's reduced to trying to bite you for damage. Plus, you can get lucky and decapitate - nobody survives that. (Including zombies... get it? Because they're already dead? Nevermind. Yes, zombies can still kill you without their head, no, the joke wasn't funny...)
In short, lighter weapons never become truly obsolete. In fact, in a way they get better: with enough enchantment, even an iron dagger can do as much damage as a valpurium two-handed sword. But, the sword does not train your dexterity nearly as much, and dexterity is (arguably) a better stat to have a lot of than arm strength.
As for shields based on what I've read, they're bad later in the game because of their lack of damage? But I was wondering if it's not their lack of damage output, but instead, there is diminishing returns for blocking value.
You're correct on both counts. Using a shield means sacrificing damage for defense, which is already problematic. To add insult to injury, however, their defensive value is highly
questionable. Certainly, early on, a wooden shield can be a great boon. But, the amount of damage it blocks is fairly low; and worse, it will break, very fast, against anything after the UT (and some things IN the UT). Broken shields are pretty useless. Using a stronger shield, such as iron, means it will function better as a shield, and last longer before breaking - but in exchange, you are stuck with a substantially heavier item with a correspondingly worse accuracy, which impacts it's ability to actually block.
Using shields made of mid- and late-game materials helps alleviate this conundrum (Do I block, and have it do nothing? Or do I not block, and have it matter when it happens?). However, by the time you get there, you can usually parry comparably well with an offhand weapon, or simply avoid the damage altogether.
It comes down to a common difficulty in building IVAN characters - tanks don't work. The game mechanics conspire to make defensively-minded equipment sets generally ineffective.
Welcome to the forum! Glad to have you. It sounds like you've got a good head for mechanics on your shoulders. I hope you stick around