@Elric Galad
Haha, funny you mention threatening presence. At some point last year (around the time I hit myself with the field boots to instantly kill myself through Barbaric Retaliation) I actually rolled in the sickening effect vs engaged targets, combining it with the no engagement vs lower level enemies. I didn't notice any imbalance because once you start to reach PL 7 (with other mods to savage defiance upgrades or other changes to earlier PL abilities) the choices become very competitive for SC Barbarian and most enemies who are dangerous by that point already resist constitution afflictions or resist all other afflictions that would have made the sickening effect more useful. The main purpose at that point was to bolster your accuracy with Brute Force vs mobs. In a team setting, you're actually applying constitution afflictions via other party members in big AoEs, so the Barbarian having this effect can be redundant unless you've worked out something for positioning.
"Off-Tanking : reliably absorb damages. The limit is : Barbarian has bad Deflection...
Only thing that they might be missing for this role is probably a reasonable Rage cost-efficiency for Savage Defiance."
While your points here are valid, the simplicity of Savage Defiance means that if you reduce its rage cost and give another survivability tool, you can overtune the Barbarian to the point of making solo easy. I tested some things regarding reducing the cost and adding in Invigorating Strike as a PL 1 active primary attack ability that grants an all-damage shield (base 5 which scales with PL) and having both was enough to create a full turtle kit that could take on all of SSS and other DLC content solo with little trouble. It's probably better to decide whether you want to introduce another survival mechanic that synergizes with Savage Defiance or focusing on Savage Defiance and its upgrades only.
"AoE Damage : Should have been of the class focus, but I would say it is only for Single Class Barbarian (Heart of Blunderbuss or Driving Roar vocal cannon). For MC, Barabaric Blow is meh and Carnage is not enough. I like spamming Spirit Tornado though : Instacast + scaling as a PL1 ability is suprisingly good for a bit of AoE DPS.
...I would advocate for a bit more cost efficiency for Tier VIII...
Carnage is good enough as a passive (PoE1 version would cause stupidly overpowered Multiclass), I think it should be supported by active abilities. However, accurate carnage is a tad weak as it is, and could be buffed a bit... maybe ?
This should be Barbaric Blow role to support the AoE component Barbarian..."
Decreasing rage cost (by 1) for HoF and IoBR hasn't had too significant of an impact in my experience. It makes HoF a little more fun end game since you have some breathing room before and after its use, and IoBR is still competing against vocal cannon shenanigans.
Yes, basically buffing accurate carnage to scale with PL and to add an increased carnage AoE component that also scales with PL fixed any issues I had with the passive while not making it feel like it had an overwhelming impact. It just made the passive ability competitive with other options.
Barbaric Blow base should probably just get a conservative change like @Boeroer suggests. Give it a push so it triggers carnage on the enemy you hit. With other changes to the Barbarian, it'll synergize nicely, especially if you do what I did and add a PL 8 ability called Aftershock that just procs a second carnage AoE.
"- Mobility : with leap and wild sprint, I think barb has what needed. Leap could be used for other purpose though...
- Debuffing / CC : should be another focus of the class... Too few effects, debuffing the same stats (not INT, DEX, CON and PER afflictions) and too much Tier 1 that can be easily resisted. Some ideas :
Leap is vaguely Okayish for 2 Rage. 6s Dazed could be replaced...
One of the Yell upgrade (Roar line ?) could be change to inflict Confuse (or Distracted, etc...).
Barbaric blow upgrades could be completely reworked to inflict a debuff... on the whole Carnage AoE. Weakened, Dazed..."
Leap is used to sequence break maps and speed run through many locations that normally can't be bypassed. Doing things like leaping past triggers, onto higher terrain (if it's programmed into the map properly) and moving more efficiently to save time during Eothas challenges. I'd say moving it to one earlier PL is about the best change you could give it. Removing or adding more afflictions to it is not needed. I've also messed with reducing the rage cost by 1, but I'm undecided on how powerful it is. On one hand, I love leaping around with such a low resource cost and being able to unload even more abilities, on the other, isn't that kind of the definition of broken? Especially for a 1 point ability? I would caution against reducing the rage cost.
Wild sprint is fine. I would focus on the upgrades because they're not worth it atm. What I did was add a charge effect where you get a bonus damage lash for 5s after activating any of their upgrades. Really awesome synergy that doesn't actually break the ability since you run out of rage really fast when doing your thing at mid to late PL anyway.
Yell abilities that confuse or distract, in my mod experience, isn't game breaking at all. The move suffers from cast time and recovery. For most of the game using them is iffy at best. Go for it.
Crushing Blow and Barbaric Smash doesn't need any debuffing mechanism. If you mess with the conditional bonus damage a little like with the gatecrasher +200% damage vs full HP target (which on testing is not as broken as it seems, especially if you take away the crit damage modifier) idea implemented by @Grape_You_In_The_Mouth in their Barbarian mod, you'll find some solid purpose in the upgrade path. The explosive keg VFX on gatecrasher is just icing. As for Barbaric Smash, you are welcome to increase the crit damage as you intended earlier. I've done the same myself, and found it to meet many thresholds for 1 rounding threats, but as @thelee pointed out it's still less reliable than a fully upgraded Paladin's FoD, so it's fine.