I would depend on what kind of weapon goes around it. If someone hits you with an axe on the shoulder the head of the axe is likely to impact first on the person than the shield if the person is not defending properly.
On the axes it looks like they went around your shield to hit you so they never got stopped by the shield. The spear I think the attack pierced the shield to hit your arm maybe, but I'm not sure if that is even possible.
It's just like you said at the moment in my campaign the empire is quite big and went with keeping the banner. I'm gonna try to with Istiana to check if the developer made and intended way for players to play at the moment. Also, She is the only character so far that I have seen with voice over.
I have been trying a couple quest in the game and so far no problems. A friend also tried this https://www.nexusmods.com/mountandblade2bannerlord/mods/13?tab=description and seems like it fixed it. The only problems so far concerning quests are "Istiana's Plan" and "Stop Conspiracy". Those quests don't seem to be fully implemented since there is no way of knowing what exactly are you supposed to do.