BPM did improve barbarians and they make fantastic fighters in multiclass builds, like brutes, ravagers, and savages are all really, really good, but this is mostly because of some low to mid level passives (one stands alone, blooded, bloody slaughter, interrupting blows, threatening presence, bloodlust) and just two active abilities (blood storm and stalwart defiance). These abilities allow you to do tons of damage, interrupt on crits, and with potions of enlightenment and high INT and perception / hit to crit you can keep up blood storm and stalwart defiance throughout even the longest fights. The rest of the active abilities, while some are fun (heart of fury, yay!), are pretty superfluous and don't really add anything to the class's utility (besides maybe leap if you can't get a movement power from another class). The tier 8 and tier 9s are especially "meh" and going single class doesn't really add anything to the awesome tier 1 to 7 abilities besides power level, which isn't as important for the barbarian as say a monk. And 33% resource regen on kill is not nearly enough reason to go SC, particularly when you can just take corpse eater and get +3 rage per corpse (though I generally prefer generic barbarian).
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Got a bit of a rant here. Was playtesting a savage (generic barbarian / generic ranger).
Overall it is a ridiculously good build, can stack accuracy + defenses with ranger's beast claw (plus marked prey etc.) and stack damage, action speed, plus good healing with barbarian. Plus 50% interrupts on crit. Build had no problem with any megabosses (minus Hauni O Whe). Doesn't even need armor.
Dorudugan was second hardest, but he goes down eventually if you can damage him fast enough while healing yourself. Anyway, I go on to fight HOW, naked because armor breaks stupid fast in that fight. I have like a 60+ roll adjustment against HOW's deflection (accuracy stacks, flanked, cap of the laughingstock) plus power of money, pes, uncanny luck etc. so I am a crit machine, and with savage hunter talent (nice improvement btw) can do decent damage even without full pen. But the pet is actually kind of a problem here because it means more symbiote procs. Killed HOW form but a massive ooze formed from symbiotes in the meantime. I kill the massive ooze and about 50 smaller ones that keep popping up. Then the two gigantic oozes, as soon as one gets to bloodied it starts merging of course, and I can crit these guys like 80% but I only interrupt half the time, either I missed the interrupt on both or one was out of range of the carnage because the bloody things insantly merged back into HOW. Hadn't really lost any resources though, blood storm only has to be cast once in this fight, so could have kept going if I had to but I rage quit. Might try it again later with a ghost heart / barbarian, or just stick the boar in the corner until there's just smaller oozes left. 50% interrupt on crit may not be good enough, even with carnage and maxed INT, which is kind of sad (would be nice if you could see the carnage effect area like in POE1). Howlers sound good theoretically (energized + carnage) but can't reliably crit things. Maybe a wildrhymer could do it with the constant energized...but wildrhymer will have more trouble with Dorudugan. Well, maybe not, that fight might be possible with legendary war bow + overdraw + energized, think that puts you at 18 pen, then use summons to protect myself. The main question is whether that can damage him fast enough. Possibly, with Sure-handed Ila.
Would be easy without abydon challenge, just use essence interrupter. Also, I recently discovered generic legendary weapons aren't subject to abydon challenge for some reason. Armor breaks down unique or not, but the generic weapons seem fine. Fists are still often the best choice but when you need ranged the generic legendary war bows are nice.
This rant does have a bit of a point. First, really like the barbarian improvements in BPM, though it could probably use a bit more. Second, Blood Storm sometimes gives way too much time for crits. Normally it gives about 3 seconds on a crit but occasionally far more. I haven't found out exactly what triggers it but I had like 20,000 seconds of Blood Storm after about 45m and just the one cast. I saw it jump by over a thousand at certain points. I think it is an interaction between interrupting blows and blood storm. Not really a problem from my POV not to have to cast Blood Storm as much but thought I'd mention it.