Wrong Tech Level

A problem I've grappled with as I learn more about ancient technologies is what we tend to think of as "medieval" is actually from a much later time period.

The knights in plate armor comes along after the gun starts to become more common.

In GURPS terms medieval is TL3 and what we think of for knights and swords and sorcery is actually TL4!

Artwork for Dungeons and Dragons and the like doesn't help much here, not that a Fantasy world needs be historically accurate.

Historical accuracy aside, if more advanced forms of armor is around, more advanced forms of weapons should start appearing.  Armor is, after all, a countermeasure to arms and improved arms are a counter-countermeasure... and so on.

What GURPS calls a broadsword's blade gets more tapered, pointier and longer.  This is because armor gets better and better at resisting cuts and a narrower point is better able to find the chinks.  The Estoc exemplifies the trend in having no edge to speak of.

GURPS: Low Tech has some optional rules for how armor behaves and makes the later weapons make more sense when the later armors are available.

But the players will cry.  They've a preconceived notion of what is correct and how it works.

Everything has a style and fashion...

If you really want to see perplexed looks of vexation on little player faces, restrict them to TL3 in a Fantasy game and keep them from the best armor.  Heck, just using the Low Tech rules for armor is enough to drive many of them insane.  Especially when they notice how little armor advanced from TL2 to TL3.  And the costs...  No steel plate at TL3.  You want plate, you're using bronze (or copper!) and you're paying a butt-load for it.

There just isn't iron plate.  Plain iron just isn't suitable for making big plates.

Steel works great for plates, but making steel in sheets is a TL4 technology.

Bronze will cost 4x as much, but you can get it at TL2!  Copper costs list price but loses one DR point.

The problem with TL4 armors is the tech to support its manufacture stems from and implies other technologies.  Which removes the world from the medieval romantic fantasy because guns rear their ugly matchlocked heads.