Like I stated before boilt and hardened and studded leather can be an extremely potent armor especially if you consider the Witcher's fighting style which will reduce most direct hits to glancing blows. Furthermore no Witcher would fall to an attack with a hammer or even a war hammer given the weapon's either limited reach or laborous process to hit. To actually pierce anyone with a bastard or even a long sword requires immense strength which is why those weapons were mainly employed to hit each other. Most significant injuries would have been done through blunt forced trauma which you would even suffer through chainmail or plate armor given that the force will be transfered from the armor to your body. Piercing mail or even leather with anything other than a short sword or a seax would have been very difficult and slashing with large swords rarely lead to cutting wounds unless you were already defenseless.True, the most a studded leather jacket (Geralt's only "armor" in the books) would protect of would be a short cutting blade... any serious form of piercing or cutting weapon would go right through... not to mention a blunt weapon like a hammer or flail. Witcher's wear leather because it's convenient, not protective.
In the game, however, they wear thick, padded leather, chain, and/or plates of boiled hide and steel... it's a design choice, but not really "canon".
Again I point to the Japanese. Most of the samurai armor was made from leather or even cloth and extremely potent at stopping cuts and piercing damage, they furthermore employed padding below the armor to stop arrowpiercing.
So in fact a proper leather jerkin or leather jacket like worn by Geralt in the books is more than enough protection for someone who will mainly deal with bites (monsters) or glancing blows or slashes (humans). Check on your medieval military history boys and girls before you put such outrageous claims forward. Even after the invention of the chainmail the leather padding beneath consisting of a leather jerkin of hard boiled leather stayed prevelent.


