I was... not a fan of those RP restrictions, because they tended to irritate and create a hassle for the rest of the party,. This basically meant that the group ALSO had to abide by many of them (no ambushes, sneaking, rejecting quests, etc). In Fate/SW, I deal with this by awarding the group a bennie/fate chip when the decision impacts everyone (usable by anyone), and the individual player the chip when it mainly just impacts them. Takes the sting out of putting up with another character's flaws.
Oh don't get me wrong, roleplay restrictions as a mean to balance a character class are pretty terrible, overall, but some still survive to this day in some form or another, because it's just something players of the game expect/want (ie, the Paladin).
I was simply pointing out that the Barbarian and the Cavalier's restrictions basically turned powerful classes into unplayable disasters fairly quickly, unless the DM took steps to circumvent their impact.
Which I had no real reason to do- I felt the classes were over...tuned, we'll say, and, at least in that era of gaming, the idea of banning something from a TSR book was a very foreign concept to the people I played with.
I didn't start seeing that sort of behavior until much later in my gaming.
In retrospect, I think in most games, the Barbarian was probably fine as a class- it's most damning features rewarded you for having high ability scores, which was already an issue with AD&D- more is more for some classes. Being allowed to roll exceptional Strength to get higher bonuses for having an 18 in the first place is an example of this, and the Barbarian gaining a d12 Hit Dice and effectively double hit point bonuses goes along with this.
The increased bonus to AC from Dexterity is a little harder to judge, since Barbarians couldn't wear the best armors to claim it. You would need a fairly high Dexterity to make your "non-bulky armor" better than the heavy plate mail of the Fighter, Paladin, and Cavalier.
The rest of the class was a hodgepodge of various random abilities, some of which would be considered "ribbons" by modern design.
A Barbarian with less exceptional ability scores wouldn't be a problem, really. But combine this with the new die rolling systems presented in the UA and things might get...weird.
I always played with the standard 4d6 drop 1 x6, though with the addition of this book, you get Comeliness, which was only used in one campaign I've played in, though it was the longest running of these.
This led to more min/max behavior, as the players had noticed Charisma was...less important in their dungeon dwelling pursuits. I was weird and hated skimping on it. This didn't have immediate payoffs, though things did improve for me much later in the game, when it became less about our personal power, and more about dealing with powerful NPC's- a factor many other campaigns I've played in have lacked.
Topic Shift: This brings up one of those things a game developer can't really balance against- how useful are some ability checks to one's game?
Almost every game of D&D is going to rely heavily on physical ability scores for combat, and mental ones for spellcasting. Saves for some will always be common. Even with light exploration, you're going to need to climb, jump, and swim from time to time.
But the value of the third pillar, Social Interaction, and how valuable Charisma is as an ability score- this is out of the hands of the developers. They can only suggest this kind of play, as it varies from group to group, campaign to campaign.
Modern game design attempts to adjust for this by making Charisma important to several character classes beyond social engagement- this unfortunately, however, leads to players of Bards, Paladins, Sorcerers, and Warlocks, being the go to characters to be able to delve into this arena with regular success- and players with less stellar checks are often marginalized (sometimes not by the DM, but themselves, as they feel their character will just be ignored, or somehow make things worse).
I often wonder if this approach is good, bad, or neutral in the attempt to balance Charisma against the other ability scores. I think it's mostly neutral, since you can't rely on the DM to make it an equal part of the game. Indeed, I know some DM's who make it an integral part of the game, but that actually leads to imbalance when you have a stereotypical 9 Charisma Dwarf Fighter with no training in social skills attempting to share the spotlight with a 16 Charisma Half-Elf Rogue who decided that Expertise in Persuasion was the way to go.
There are, thankfully, other forms of interaction with NPC's that require non-Charisma checks- knowledge skills or Insight, but if your class doesn't particularly favor Intelligence or Wisdom, you might find yourself in trouble here as well.
Then add onto this the classic love of the game to have spells as "I win" buttons, and it becomes apparently how easily a Fighter could become marginalized outside of the Combat Tier.
Note, I'm not saying he will be as a matter of course- even though I and others have seen this play out, it's not universal. Many campaigns have Fighters able to interact with all aspects of the game well.
But it just goes to show that balancing the game's rules
well (since you can strive for perfection, but will never reach it) is only half the problem. You also need to give the DM/GM/Referee/Storyteller/Judge appropriate guidance so that they will use what is given to them properly.
And no matter how well you accomplish this, the old adage about leading a horse to water still applies. That doesn't mean that building the game well and teaching people to play well isn't a worthy effort- it very much is!
But there's always going to be situations where even the best game ever made will result in a mediocre experience for those involved. Some people look at this and say "balance isn't important" as a result.
But if a well-balanced game is no better or worse than an unevenly balanced game, then why spend money on game books? We could just as easily play Cops and Robbers and resolve "I shoot you, you're dead" "Nuh, uh, I ducked behind cover!" with the flip of a coin.