Armor isn't 1 size fits all, its usually tailored to the person. There's also a misconception about armor and hardness and tensile strength > padding. Padding/under layers is actually the more important component of armor as it is the layer that dissipates force. Even tanks work the same way with energy dissipating rubber/inert gas layers/empty space/dense materials. The surfacing material's main job is to stop penetration, the under layers stop energy transmittal.

In an environment with mostly glancing blows and large shields, you don't need to be protected with the absolute best surface/stopping layer. So things like linothorax are perfectly fine if you are fighting at range or in one direction in a not super duper lethal environment.