With 100 or so less paragon than you have, I cleared a solo GR128 on my WW/Rend Barb… https://i.imgur.com/7gN2Mdz.jpg
You might find this a useful read…
You’ll find numerous Barbs only too happy to offer advice / answer questions you might have. Currently discussion in there is surrounding which follower to take to be most effective solo after Patch 2.7.0’s follower changes hit live.
The higher you go with WW/Rend Barb, the more you need to group up big packs of mobs. Players that are newer to the build underestimate what this means, in terms of numbers of mobs. We’re talking about multiple screens-worth of trash mobs, and preferably 3-4 elite packs. You drag them with you using Ancient Spear / Rage Flip, and then clump them up tightly using Ground Stomp. Ideally you want to drag them right up to a nicely placed Conduit circuit and melt the lot of them. Also when you manually cast Rend, those Rends benefit from Area Damage (which is why Ground Stomp pulling lots of mobs into you, to maximise the number of mobs you can hit with it is important) whereas the auto-cast ones from Ambo’s Pride do not.
Rule of thumb… if you have less than 200 trash mobs in the pack, get more. 