TwoSix
Everyone's literal second-favorite poster
But here's the thing. Parity, verisimilitude, genre emulation, drama, and system mastery are all on a spectrum. Prioritizing one or two doesn't mean my tolerance for the loss of the others is infinite. It means I accept that to achieve greater fidelity to one priority, there will be tradeoffs in my ability to realize the others. It also means accepting when I've reached the point of "Good enough" for the main priority, and can give more attention to some of the lower-priority options.
Parity and system mastery are two of the options where tradeoffs may be necessary. Obviously, one can have a game where build parity is exactly equal, by giving every player the same character. Then system mastery of at-table play (plus random chance) becomes the only determinant of a successful outcome. But virtually no one wants to play a RPG with no character options at all. So we add mechanical widgets to the characters to allow differentiation. And if there is a mechanical system, it's assumed that this system should provide something meaningful, which in the case of an RPG, is a greater chance to impact the outcome in a chosen direction. Thus the desire for meaningful character build system mastery.
Now while rewarding system mastery for character building is a straightforward mechanical exercise, it sits in tension with a group of other RPG design pressures and tensions. We still want to reward at-table play system mastery, which means any character build that exceeds any and all at-table challenge can't be allowed. (See Pun-Pun).
We (often) want to enforce genre sensibilities, which means refining the character build options down to a more limited set. Simultaneously, we want to respect player's aesthetic choices, which means we want to give players the ability to build a character that they visualize. Obviously, these two options often come into conflict, as genre definition is very nebulous and varies between individuals. Equally, genre simulation can either prop up or attack the individual's sense of verisimilitude. Respecting an individual's aesthetic choice for character can often clash with another individual's view of the game world. This sets up conflict like the halfling barbarian, especially when mechanical constraints on the genre simulations are seen as key reinforcers of verisimilitude.
Additionally, as most RPGs feature cooperative parties of players, there are tensions found within team play. In general, while most people want the team to succeed and are willing to subordinate individual goals to seem the team goals met, that doesn't mean that people want their individual efforts to be overshadowed. These orthogonal goals create some of the tension on the spectrum of effectiveness that plagues discussion of 3.X and 4e. Some people feel that individual efforts should be highlighted and generally equitable (parity), while others feel that's a lower priority goal when compared to enforcing genre conceits and versimilitude. Some people that parity should only be based on equivalent system mastery, while others feel that a player's individual aesthetic should be a higher priority than system mastery.
tl;dr: In-party parity, rewarding system mastery, versimilitude, genre simulation, and freedom of character choice are in tension. Pick some, lose others.
