After UA 5, I made a spreadsheet to examine the impact of the changes on damage potential. I made it primary against target AC because I was most interested in the scaling effects of the changes to the Great Weapon Master feat compared to the new versions.
As that's kind of all been resolved, I've rewritten it to see the scaling across levels. I did check with varying base accuracy levels, but the curve's shape remains pretty much the same throughout, so I'm not worried about that side of things. I used a base accuracy value of 60% (ie: succeed when you roll an 9 or better) to match with Treantmonk's and others' assumptions on their estimations, though I'd prefer a 65% base.
I set up four configurations. All comparisons assume Rage is always on, and Reckless Attacks is always used. This uses the Berserker subclass.
- UA PAM: This uses a glaive (Graze mastery), and picks up Polearm Master at level 4, Great Weapon Master at level 8, and Charger at level 12. It starts at 17 Str, gets 18 at level 4 with PAM, and 20 at level 12 from the combination of GWM and Charger.
- UA DW: This uses dual wielding, with two shortswords at level 1. At level 4 it picks up the Dual Wielder feat and changes the main weapon to some versatile d8 weapon. Charger is picked up at level 8, and level 12 caps Str at 20 using some undefined ASI or feat. It does not have the Two Weapon Fighting fighting style since that's no longer available as a 1st level feat.
- UA BA: This uses a battleaxe in one hand, and a shield in the offhand. He's picked up Sentinel and Mage Slayer at levels 4 and 8, and Great Weapon Master at level 12 to cap off Str at 20. This isn't the best subclass for a more tanky-focused barbarian, but it can at least show where a one-handed build is at compared to the others.
- UA GA: This uses a greataxe (Cleave mastery), and picks up Great Weapon Master at level 4. Level 8 just raises Str to 20, but using half-feats at 8 and 12 instead doesn't really change much.
As you can see, the curves are all quite similar, just offset a bit. The greataxe and dual wielding start off slightly better, with the glaive jumping up to join them at level 4. From level 5, PAM and GWM are pretty much on par until level 12, after which PAM pulls ahead.
At level 10, damage ranges from 32 to 48 DPR. At level 13, where Treantmonk likes to compare, it ranges from 47 to 67 DPR.
For reference, here's the damage curves with Reckless Attack turned off:
At level 10, the damage ranges from 15 to 30 DPR, and level 13 ranges from 22 to 42. Reckless Attack contributes about half of the Berserker's potential damage (though slightly less in the PAM build).
Putting aside the one-handed battleaxe build, the other builds put up respectable numbers and keep fairly close together.
Also, for the issue of Brutal Critical, I made a version where PAM got 0 from brutal critical across the board. You can see it drop from modestly above the greataxe in the upper levels (in the earlier image) to almost even with it. At level 20, it drops from 84 DPR to 77 without Brutal Critical, so Brutal Critical is about a 9% increase in total damage by the end. (NB: Flex was about 10%-12% increase in damage.)