The seeds for the (generally) poorly received fighter classes in Unearthed Arcana were sown in the earliest days of the game's history and the Barbarian class eventually presented represents the "victory" of one of two strands of influence on the game which represent by far the biggest flaw in the design philosophy of AD&D (and to a lesser extent, OD&D).
As any fule kno, D&D grew out of mediaeval wargaming and this brought with it a certain attempt at simulation in things like armour types, weapons (pole arms!), movement rates, encumbrance, and so on which was based on the real world, at least as far as the designers could make it.
But the players and designers in those early days also wanted to simulate something unreal - they wanted dragons that can fly and breath fire, trolls that regrow limbs, fireballs and lightning bolts (very, very frightening me - Galileo etc.) and other magic items.
These two design aims did not sit well together, not least because the fantasy side of it is much more subjective. It's certainly subjective what parts of the real world one thinks worth simulating in a game, but at the same time there is a basic testable nature to those parts that fantasy does not have and nowhere is this more clearly seen than in the case of the world's favourite barbarian.
Bar Bar Bar
"Barbarian" means to many players, and even moreso in the 70's, "Conan". What does Conan look like? Well, he's big, has blue eyes and black hair, is very strong and wears....? Well, in the books he generally wears armour, usually chainmail but sometimes in hot climes he will eschew the weight for mobility. But that's not what people tend to think of when Conan is mentioned. They tend to think of Conan as depicted by Frazetta and his imitators - naked but for a loin-cloth or sometimes not even that. Simulating one Conan doesn't necessarily give you the Conan your players expected.
Flicking through Judges Guild material such as the City State of the Invincible Overlord will turn up any number of such "no armour barbarians" in the illustrations. It was a big trope from the very start of the game's popularity. Very big.
The magic shield in particular is a classic "unintended consequences" moment. It disrupted both realities in the game - the real-world reality and the fantasy one.
Imagine AD&D without magic armour: two players roll up identical fighters and play them, one aiming for playing a Knight (ie, Cavalier) in shining armour and one as a Barbarian in nothing much other than a red cloak. At early levels the would-be knight probably can't afford the best armour so the mechanical difference between the characters is minor in combat. As the knight gains levels and better armour, however, the barbarian's choices start to balance out - s/he has better movement and potentially gets bonuses on reaction and missile fire which the knight loses as s/he dons bulkier armour, even visibility is massively improved and listening at doors etc becomes an instant action.
|Insert "Ogre" pun here|
|High level fighter|
[check this - ed.]
Now add in magic armour and the barbarian is dead in the water. Magic armour is listed as being like normal clothes and either weightless or half the normal weight. There's been various attempts to work out what this means, but it certainly erodes the barbarian's mobility advantage. Much worse is the effect of combined armour and shield magic. +3 on each is not unlikely for 8th level characters and the barbarian superhero is suddenly giving up not 8 points of AC to the knight but 14!
Who's Cockamamie Idea Was This, Anyhow?
PHB-era AD&D simply does not support playing as a barbarian, and it has a lot of trouble with playing as Robin Hood too, but if you keep such a character in the wilderness and lean heavily on missile combat I think it's just about doable.
I say "PHB-era" (just there above, look) but really the issue is the contents of the DMG. Well... I say the DMG, but actually the issue is the contents of most of the TSR modules. The level of magic treasure in the 1e DMG and MM is very low compared to the modules from which many DMs learnt their ideas of what a haul of treasure looks like. The books didn't really back that up.
For example, a medusa lair has no chance BtB of containing any magic armour at all. If an 8th level fighter is encountered via the "Men" entry, far from "+3 on each is not unlikely" for armour and shield, there's only a 16% that s/he'll have both a magic shield and magic armour of any sort and a very remote chance that they'll both be equal to +3 plate+shield or better (about 1 in 33, for a total chance of less than ½% of all encountered 8th level fighters).
Anyway, what the books said and what the modules did were two different things and the modules won because, firstly, Gygax wrote most of the iconic tone-setting modules and they reflected his style (who's style do the books reflect? Good question), and secondly modules were wildly successful in the early days of the hobby and literally millions of players and DMs formed their expectations of play from them and not from using treasure types and listed chances for items from the monster manual.
|A nice knight in|
in front of the fire
And yet...The barbarian fighter is one of the stronger archetypes in fantasy, particularly art and film fantasy. Much moreso than clerics or monks, or even rangers. Clearly there was a problem with a game which was unable to allow players to successfully participate as one of the game's own inspirations.
Thus we arrived at Unearthed Arcana which so sharply drew the line between the Cavalier and the Barbarian and which, rather than mechanically reining in the former (which would have required a drastic change of direction for the whole game by that point), the latter was boosted to give balancing advantages, not least in the areas of AC and hp, in an effort to make the trope playable.
In the end, the attempt largely failed and the UA barbarian and cavalier classes have never really caught on. The cavalier was unneeded - the game actually allowed a player to play a typical knight from the first day of publishing - and the barbarian's "solution" to the problem felt artificial and forced and both classes were far too heavily encumbered with rules that got in the way of player interpretation.
|Classic D&D Thief|
|More realistic thief|