I think the issue with barbarians is only partly due to the class itself and partly due to how endgame is run. I'll take a barbarian over nearly any other class from level 1 to 5, maybe even higher. Boosted run speed. 2 cleaves. Pile of hp and potions to cover any healing of buffs needed. Even up to about level 10 this strategy remains valid though to a lesser extent. Once pot healing can't keep up, you need to explore other options which can lessen your DPS to some degree. By the time you get to epic elite, you have twisted the barb into something that doesn't quite function the way a pure barb does or you're bringing a healbot. This is the state of the game. Most effective endgame epic elite builds have self healing in burst form which can be repeated over time. Heal, Reconstruct, etc. The days of having a dedicated healer in 6 man groups are gone for many, making the barb's rage ability a liability in many cases. Your options are chug SF pots the whole quest or give up raging for cocoon and/or scrolls. Raging also has to be worked around if you want to keep self displacement up for all fights. Other classes don't have this limitation to work around. Either click or scroll cast and engage. Not so for barbs.

One could play a barb in a different fashion. Functioning similar to a rogue where you strike hard from behind, minimizing incoming damage. In epic elite, you will still take boatloads of damage. It's just the power that the mobs hit with. You need a burst heal when you get hit a couple times.

There is the virtual price you pay for taking barb levels as well. You give up monk levels which are very much in flavor these days for multiclasses. It's very hard to beat Shadow Fade for defense in addition to evasion and up to 3 extra feats. You also give up paladin which seems the easiest way to get workable reflex saves for new epic elite content.

Barbarian has so many aspects of the game working against it right now which makes it a hard class to play. It has limitations that just don't exist for other classes and combinations. You can play it, but you feel like you're tied down, not able to get the most out of the build, simply because the game has evolved to prioritize things the barbarian does not do well.