In pretty much all but the most dedicated D&D fantasy novels (and pictures and to some extent movies) no one wears armor. I admit that is a pet peeve of mine. But instead of complaining about that instead I want to talk about some different systems and whether one could get away with a melee fighter without armor.
In thinking about systems I have some what landed on the concept of skills and how they are handled in a given system. Because the more emphasis there is on Skills, over arbitrary things like levels or completely falling back on attributes, it seems it is easier to get away from the basic idea of a warrior in armor will crunch the one with no armor.
For example, on the one side of things, is D&D 5E. If you want to know if you can hit something or not get hit it is really just a matter of Armor Class versus Level. If you are low level, chances are you will not be able to hit a heavily armored opponent. Which is fine, it works, and is consistent. And bear in mind I am talking about hand to hand melee, not archers or magic. While you could construct a lightly armored fighter in 5E, chance are you would spend your lower levels running around and avoiding close combat.
Of all the other systems I am familiar with, the opposite is GURPS. This is a system where what you can do is pretty much all about your skills, when you get experience you improve your skills. There are no levels. But if you are a highly skilled fighter you can get away with light or no armor, as you can Parry, Dodge or Block your opponents attacks. This is probably why I think the GURPS Conan book is one of the best Fantasy systems out there as far as matching flavor to execution.
What got me to thinking about all this is I am re-reading the Wheel of Time series. And that is a high fantasy series, where very few people wear much beyond a breastplate. And you simply could not get away with trying to recreate that world with D&D. (On the other hand the GURPS magic system is so antithetical from the WoT series that you could not use that system at all.)
And then I have been watching an interesting series on History channel about blade smiths crafting weapons. And it occurred to me, comparing the katana and the crusader sword, that muc of the difference between the two was simple geography. Japan was not rich in Iron ore, and therefore it did not make economic sense to have people try to wear heavy metal suits of armor. Therefore the katana was all that was necessary against the types of armor available.
And I thought about creating a campaign in that type of land, where steel weapons and armor are just not common place due to lack of materials. Again I could maybe get away with this with GURPS. But I could not with D&D or Pathfinder, because the monsters and level issues would create vast gulfs. How are you supposed to survive a swipe of a dragon claw in D&D without heavy armor?
This all reminds me of when The Matrix first came out. And one of my friends was trying to figure out what system would best match up to the action in that film (Shadowrun BTW, it’s the only system I know of where a single character can perform multiple actions before anyone else goes.) The point being, while it is important to have a group of players with similar knowledge of a setting before starting a game, it is even more important to match the system with the setting.