Ya, i need the same advice as well for my season barb alt that I just leveled yesterday. I tried WW and Raekor6 (without vileward) for 55, stuffs are not dying at all.
On the other hand, I had a non season barb with fully optimized stats ancient, partially augmented, I was able to clear 71+ for both R4IK6 and leapquake, but I have trouble on season just to clear 55 with zero ancient item but with the level 70 gems from my DH. I have a feeling that leapquake might clear 55 easy without ancient items but my set is not complete.
So if you are trying to clear all 4 sets at 55 wastes is by far the hardest.
might of the earth - use leap quake build = easy
imortal King - use chainer's raekor build (raek4/ik6) yes RORG counts, as long as RORG gives you 6 peice bonus.
raekor. - run chainer's build verbatim, but swap out 2 peices of IK for Raekor so now you are doing IK4/Reakor6. The only real difference here is that a lot of your damage now comes from Boulder toss- so you have to aim the Boulder toss well. If you could do GR 60 with rk4/ik6 then you should be able to do GR 55 swapped, and same build.
wastes. By far the hardest. You need semi decent gear. Run 6 peice wastes and bulkathos for weapons little rogue and slanderer could work too. Left click furious charge merciless assault right click WW blood funnel. Cube furnace, mantle of channeling and band of might. Where FNR as the rings and use furious charge to give you the generator bonus on the ring set.
The rest of the abilities you can play around with but typically you want to use the shouts. Threatening, falter. Battle rage bloodshed, war cry veterans/impunity. If you can fit it in your bar, add rend mutilate just because of build synergy. If it's still isn't enough, level a taeguks, and maybe a pain enhancer.
I cleared a GR 55 with 3 minutes left with basically no ancients, but gear was enchanted to get better rolls. Paragon 700, Lvl 70 gems.