Physical regional damage has always been dodgy/approximative, in Warband and in Bannerlord. I suppose the devs want it like that, it's not realistic combat.
Same with the shields, their covering area is an invisible veil that you can't really guess. If you try to aim the legs or even foot of a sturgian spearman while he has his round shield on top of his head you have 80% chance of your thrust boucing on...the shield
RBM mod improves this a little bit but shield and armor coverage are just some weird tweaks calculations and not wht you see on your screen.
It's a bit of a shame because there's little incentive to carry a heavy (supposedly) full covering pavise if the tiny eastern round shield covers pretty as much.
As for the looters, they are by design hard to kill in the very beginning of the game (Warband was like this and I think I like it that way). But if you learn how to fight in the game and count on your tactics skill (the ones in your brain, not the perk branch) and your mates you will quickly crush them like butter. (and normally you don't have access to a steel helmet at this early stage until you managed to kill sea bandits, wich are a tougher kind of looters).
Also ask riot police officer what a stone thrown at your head feels like while you're wearing an helmet...it's not fun at all
