Throughout the game's history, builds have been made with the intention to operate most efficiently within its current environment. The aim will always be towards higher damage output, higher spell DCs, higher spell penetration, higher saves, higher player damage mitigation, fastest quest completion. "Character Balance" is a current reference point as to what will happen with player abilities in the next update. Players who have found the best "balance within the current environment" are deemed overpowered by others who either didn't figure it out first, or who have decided that some abilities should simply not exist in the game. The point remains the same: most efficient within the environment. There's a reason warforged pick barbarians are not the frontline in epics anymore.
The previous best reference point was Epic (prior to its changes). It was the target of many discussions about how a player could operate best in the game, and many builds existed with the main goal of operating within epics. Now, the current best reference point is Epic Elite, with its combination of incoming damage & its mitigation, saves requirement, offensive spellcasting requirements (DCs & spell penetration), healing needed, & player damage output needed for a timely completion. It is also a good reference point because of the majority of player's benefit to running only elites (Bravery Bonus, XP rewarded, named loot, Commendations of Valor, max favor). These incentives have made elite (especially Epic Elite) the most often run difficulty in the game, & Epic Hard & Epic Normal run mainly for a quick completion either for a raid flag, raid completion, or fast XP.
There is an issue with Epic Elite. Yes, it should be difficult. But there is a difference between challenging & suffering. The difference between Epic Hard & Epic Elite is significantly larger then Epic Normal & Epic Hard. Elite, on the quest entrance screen, states that it feels like a quest 2 levels above its difficulty on normal. However, a level 22 quest run on Epic Elite does not feel like a level 24 quest on Epic Normal. The monster hitpoints, saves, & damage output in a Epic Elite level 22 quest is much higher than monster hitpoints, saves, & damage output in an Epic Normal level 24. This means a much higher investment on the part of players to find builds that operate well in Epic Elites (massive damage output, insanely high saves/hp/sp, self healing, maximum spell DCs & spell penetration, as much miss chance gear as you can get (Ghostly, Blurry, Dodge, & PRR/AC if you can spare it). The squeeze on resources that Epic Elite has pressed on those who run it have created the new builds that survive best in them, & are therefore blazingly powerful on lower difficulties.
The dynamic between the game (& those who design it) & those who exist within it (the players) is one of Selective Evolution. The builds no longer capable & efficient in the game have gone extinct; outrun, out-survived, & out-built by new recombinations. This will always be the case. There is no true balance between player & player, the balance exists between the player & its environment.