Lets compare some ability tooltips here. These are taken with approximately 4800 weapon damage, 32.8k stamina and with the Slimecraw set.
(And remember that the PTS rending slashes has its initial bleed damage tick delayed so you can no longer spam it and have those bleed ticks happening. The main reason why it is used in PVP now in live is because you can spam it and get those bleed ticks between each use. Its snare is also often made redundant especially in group situations (which is what the majority of PVP takes place) where AOE snares are a lot more effective, and its increased PTS DOT damage is countered by its increase of the PTS DOT duration. And these new AOE buffs will not stop these DOTS from being used as a potential spammable).
(I'm also on a DK so its important to take into account the 2m extra range on rending slashes and claw)
RS compared to Carve:
Carves direct damage portion does about 31% more damage than rending slashes direct damage.
Carve is a 7m
AOE cone, rending is a single target 5m ability.
The difference in DOT damage is marginal. The carve DOT can also be applied to multiple targets at once unlike rending slashes. Carve DOT is also bleed damage!
Carve can be greatly boosted by the masters weapon; it has far more DPS potential than a masters dual wield rendings would ever have.
Rending slashes is cheaper...and it also gives a 4 second snare for a 10 second DOT, its only real positives compared to carve.
RS compared to Obnoxious Breath:
Noxious does about 34% more damage than rendings if you compare the direct damage portions.
Noxious is a 10m
AOE cone, rending is a single target 5m ability.
Rendings DOT damage is about 20% more than Noxious, but the Noxious DOT can be applied to multiple targets at once. The Noxious dot is also poison; so while It can be mitigated, it is able to proc poison status effects which can increase the damage.
Noxious gives major fracture to all targets hit.
The snare from rendings is only a little better than the Ardent flame passive snare you can proc with noxious.
Noxious is cheaper with DK passives.
RS compared to Venomous Claw:
Rendings does 15% more damage than claw when you compare both the direct damage portions.
Claws tooltip DOT is about 9% more than rendings, but when you consider the fact that its damage increases with every tick, Claw begins to do noticeably more damage than rendings. It usually ends up being about being 30% more DOT damage after a full DOT duration (at least in my case).
Claw is less than half the costs of rendings after DK passives.
The snare from rendings is only a little better than the Ardent flame passive snare you can proc with claw.
My proposal is to increase the direct damage portion of rending slashes where the sum of both those direct hits is about the same as Carves direct damage. Rendings has not only taken a big hit due to the delayed initial bleed tick, but it also made noticeably weaker compared to other newly buffed abilities. This way If rendings were to do the same amount of direct damage as carve, the difference is that rendings would be cheaper and provide a snare, but carve is an AOE with greater range (except for DKS) that is able to effect multiple targets at once. It is important to take into account that the target may have major evasion which can reduce carves damage, but AOEs also cannot be dodged and they are useful for taking NBs out of stealth as well.
Noxious direct damage would be a little more, but it also gives major fracture and is a DOT with 10m cone range. Its DOT is a little weaker, but against multiple targets Noxious has greater damage potential than rendings.
Rendings would do about 50% more damage than claw when it comes to the direct damage portion, but claws DOT is also a good amount stronger, also procs a snare, can proc poison status effects, and is less than half the cost as well.
Edit: Grammar. And forgot to add the snare when comparing rendings to carve.