I did a full playthrough on PotD with a Barbarian/Fighter main character, and I didn't find any point to the Barbarian abilities. They all had a marginal impact. The only reason I picked Barbarian as one of the classes was the higher health pool.
The Barbarian passive abilities are insane for pretty much any character.
The problem is not whether they are good or not, the problem is they are not enough to base an entire class on. The passives could've easily been given to a Fighter subclass, remove that regen ability, add Carnage. If I had a say in the class design, I'd remove Barbarians, Monks, Druids and Rangers, all superfluous and unnecessary classes in the way they are implemented. Give the spiritshift form as a spell to Wizards (polymorph self), Monk and Barbarian could've easily been Fighter subclasses and Ranger a Rogue subclass. Focus on the classes that are left and make them more diverse. I'd also place restrictions on armor and weapon use. "But my choices" I hear you say, well that's where the multiclasses come in while making the classes themselves more diverse. PoE's system plays like a classless one due to all the homogeneity. The only unique classes are Ciphers and Chanters, everything else is a reskin of everything else.
The builds which are interesting are suspiciously few and far between for a system with so many alleged options. In PoE1, there are 4 I can name - Barbarian focused on dying and triggering on-knockout abilities; Skaen Priest; Rogue focused on casting from scrolls; and dual Ciphers which trade their buffs on each other. If you browse the build sticky on the Obsidian forums, you'll notice a lot of builds using same items and same kind of feats and talents. In PoE2, there are even fewer interesting ones due to the removal of many unique abilities on items and subclass abilities (like Skaen sneak attack, which I'm still not over *twitch*). There are still a lot of clearly superior options that get used in builds constantly. This also contributes to classes feeling samey and playing the same.