The Philosophy of Inverted Classes

Turning the Barbarian and the Cavalier into Fighter variants with only one major improvement and a couple interesting limitations seems like a great fix. But, like the Fool and the Tourist, the more interesting part is the inverted prime ability. The Unearthed Arcana Cavalier in particular has a whole bunch of minimum ability score requirements in order to justify cranking up their class abilities. AD&D in general pretty much has a minimum ability score for every class. Even OD&D has several classes with minimum ability scores. The result of that design decision is that players who roll average scores feel cheated, and even one slightly low score with no real high score triggers cries of "this character is hopeless!"

By including classes that have no minimum scores and that use an inverted prime ability scheme for the experience bonus, players have an interesting option. For example, a player who wants to play a Fighter, but who has a low Strength, might feel that they would be penalized for playing what they want to play. Adding the (inverted) Barbarian and Cavalier gives them two classes that are basically just Fighters, but shifts the prime ability to Intelligence or Charisma and inverts it, so that they may even benefit from playing a supposedly sub-optimal character.