One way to promote balance in rules is by imposing bans: items, skills, or styles which won't be allowed in a competitive setting. These bans must be made tailored to the top level of play in that top players under these restrictions can compete in a roughly equal footing provided everything else is maxed out (e.g. maximum stats and player skill). Of course, bans must be tested and in general, there must be as few bans as possible to keep the game diverse.
I will now propose a set of bans for skills, styles, and items which I have deemed to be too powerful or remove the player skill element from the game.
Cloak - Blackfeather: This item is very strong against ranged attackers who use projectiles as their primary form of damage. The rockets do very high damage and home-in on the attacker from any range (even across the entire chapel). These rockets pose a great threat to other DH, Wizards and some other classes relying on projectiles in their build.
Set - Danetta's Hatred (2pc): The set bonus provided by both of these allows the DH to use Vault almost indefinitely. Due to Vault possessing many invincibility animation frames, most players cannot harm the DH with anything during Vault, including all CC abilities. Furthermore, the set also allows the DH to stun and leave a clone behind with every Vault, adding to the confusion and dispersing homing attacks. One weapon of the Danetta's set should still be allowed since the DH cannot Vault indefinitely in that case, just the use of both should be banned.
Ring - Unity: This ring has very peculiar effects when used in the chapel with other players. If only one player is using a Unity, then there is no issue. But when more than one player uses it, the effects can be absurd. To prevent the issue where both players want to use it for the stats but not the secondary effect, in fairness, both should not be allowed to use it.
Shoulders - Homing Pads: There should never be a reason to warp to town in a competitive match but the large damage reduction is often abused if a player stutter steps the portal animation during an attack by another player.
Shoulders - Pauldrons of the Skeleton King: These shoulders randomly prevent a player from death and can proc more than once in a battle. I am not sure of the internal cooldown, but death prevention adds a random unnecessary luck element to the game which should not be in a tournament. Items with a death prevention ability on a long cooldown which are not random should be fine (e.g. Firebird set bonus).
Set - Jade Harvester (6pc): This WD set bonus is only very effective versus classes such as Barbarian who cannot avoid the damage and will almost certainly be killed in a single hit. Such one-shot builds are not recommended for fun play. An alternate rule could be to simply ban the Creeping Demise passive but allow the set.
Voodoo Mask - Quetzalcoatl: This WD mask enables Haunt and Locust Swarm to do their full damage over half the duration, effectively doubling their damage! This item enables WD to build far more defensively while still delivering an overwhelming offensive game, specifically Haunt does 666% damage per second with this (compare to Rend - Lacerate 270% per second)! I am not 100% sure if this needs a ban yet, but it is on the table of considerations.
Set - Natalya's Wrath (4pc): This old legacy set grants a DH with near unlimited discipline and enables the infinite chained Smokescreen build where the DH can remain invincible indefinitely. This is by far the most broken build in PVP at the moment since one player remains 100% invincible full time!
Amulet - All Elemental Absorption Amulets: All of these amulets: Talisman of Aranoch, Countess Julia's Cameo, Mara's Kaleidoscope, The Star of Azkaranth, and Xephirian Amulet, provide an immunity to a particular element which may completely shut down a class's offensive options. For example, WD rely heavily on Poison and Cold damage, so a player using one of those amulets could remove the threat of one type of damage while stacking resistances for the other type.
This list needs a lot of work since I do not know many of the other class match-up problems (I am most familiar with DH). I do however recommend banning the Lingering Fog rune for chained Smokescreen for extended duration with enough cooldown reduction. There should always be a window for players to damage each other between activations. Also, the WD's Creeping Demise passive should be banned in some match-ups since it favors an apply it and run away strategy; which is very non-confrontational and leads to boring matches.
Non-confrontational or bunker styles should not be allowed. This includes camping the western island, setting up an array of sentries or traps and not moving out of range of them, or refusing to engage another player for extended periods of time while waiting for a lengthy cooldown to refresh.
This list of bans or restrictions is by no means a complete list and most of these have not been fully tested. I am merely writing here to post my thoughts on a step in the right direction to make the completely unbalanced "brawling" system more fun for everyone.
If Blizzard doesn't want to touch this aspect of Diablo III, then the task is left to dedicated players who want to have fun in a non-frustrating and somewhat "more fair" environment.
If you have comments or suggestions about some proposed rules or new ideas, feel free to post and we can together try to make the brawling aspect of the game more enjoyable for everyone.