Good discussion here.
I'd like to weigh in.
I think some of you are misunderstanding the reasons some things were invented. Especially in the warfare department. Take the crossbow for example, while it does have a lot more power than the standard bow, this was a secondary improvement over the fact that anyone could fire a crossbow affectively, while only a person trained with a bow and with a strong enough arm could fire a bow affectively. The true advantage of the crossbows the reduced training time required, increased short range accuracy and finally the improved power and armour piecing.
I also believe that siege weapons like the catapult (If I remember correctly the Aleithi have a type of catapult using a fabrial) or even the cannon were not invent to kill more soldiers, they were invented to cause holes and damage in city walls. While a shardbearer can jump or climb up a city wall easily while weathering the hail of arrows, they wouldn't be able to take a city on their own. Somehow armies in Roshar need to deal with walls, so I don't see why there wouldn't be people inventing things to destroy or scale walls, and therefore siege equipment
This all being said, the best point within this thread are that fabrials would be distorting the way science developed over time. Instead of thinking of ways to launch a large stone at a wall with physics, the engineers of Roshar would be thinking of ways to use fabrials to achieve the same thing. The result being that certain inventions in our history which are variations or items based on others wouldn't be invented because the required understanding of physics is not being developed due to the magic system in place.
So yes some engineers would be thinking about how to kill a shardbearer, so they work on fabrial shields or similar. Others would be thinking along other lines. like, how can we scale that wall around Kholinar? or how best to kill all the spearman around a shardbearer so we can focus on him after.
Also some of you forget that engineers don't know the effectiveness of their inventions until after. So stating that inventing the cannon is meaningless because you can't hit a shardbearer for reasons 1 through 4 makes no sense, because how is the engineer trying to figure out how to fire this ball of metal 100s of metres going to know his final product is going to be difficult to aim and slow to reload?
TL;DR: Inventors usually work around one problem they see in the world and invent something to resolve it. E.G the crossbow because bows required too much training and skill to use well. The warfare parts of this discussion seems to think all military advancements were pure up the kill rate inventions when most RL military advancements were not.
The Magic system is place will change the way science develops on Roshar as opposed to RL. However the same problems exist so alternative inventions should be popping up.