If you looked at raid DPS calculators, you would see why. In a good group, TA can give ~900 rDPS to 7 other people. This game is all about damage, since healing is overpowered, and enmity is a joke for any tank that knows a proper opener. The only thing left to focus on for tanks and healers is damage, just like the 4 DPS in the party. So the meta stacks rBuffs to give the party more damage.
That being said, Disembowel is the real culprit in terms of the current meta at hand—where as TA can give anywhere from 90 DPS to 150 DPS to a single person, Disembowel gives ~300 DPS: it’s +5% damage for the entirety of the fight, which is why BRDs and MCHs that care about their damage will always want a DRG with them, and any group running BOTH BRD/MCH would be out of their mind to not bring a DRG for that +~600 free rDPS.
As for the OP’s suggestion, I disagree with it, mainly on the account that resistance down debuffs should not even be included in these new “role actions”. They are all redundant at this point, with only BRD/MCH being unable to apply their own, and should be removed entirely in 5.0 — with minor adjustments to DRG’s damage, since they will be severely hurting at that point, and maybe a slight tweak to at least MCH, who is already getting replaced in speed kill comps by BLM or SMN, and who severely lacks in both utility and damage. BRD may have low damage, but it is the master of utility (and always has been since 2.0) so it can at least compensate in some shape or form.
It is also worth considering that this would just cause more of the same issues that the current role actions have for some jobs, in which there are no “options” in terms of what to bring, only the illusion of it. For example: physical ranged have 2 mandatory skills (Refresh and Tactician), 1 semi-mandatory skill (Palisade—for physical damage), and 2 skills that they usually prefer to have at all times (Second Wind and Invigorate); the remaining skills are either useless in combat (SWIFTSONG—never not going to call Peloton that), highly situational (Head Graze), or completely useless (Leg Graze, Arm Graze, Foot Graze—I put Arm Graze in here not because the stun is worthless per say, but that it’s never been used since 4.0 launched, and other jobs already have stun options—only physical ranged have a silence outside of NIN’s Jugulate, and tanks can bring something more useful to them instead of Interject). Adding something like Foe Requiem to their arsenal would just further remove the illusion of optional role action skills, and put another mandatory skill in there.
Literally the only two that don’t have them are BRD/MCH—all other DPS (and WAR) can apply the resistance downs the buff their own damage. And since Yoshida has already said that he is not okay with BRD/MCH being OP and having their own piercing (yet perfectly fine with them being OP with a DRG in the party), they aren’t getting their respective damage downs. And if they did, then the debuffs are just redundant since they will never not be on a boss. Might as well remove them from the game from that point.
Sure you can argue to give piercing to RDM, but I would be more for just removing them entirely. They were something that should have gone with 4.0’s release, rather than have 1 nerfed by 5%—which didn’t destroy the physical meta at all until BLM and SMN began to pull enough damage to replace MCH (BRD didn’t go anywhere).
That still doesn’t answer the piercing problem with regards to BRD, or with MCH’s other active time this is not spent Overheating. I stand by what I keep telling you in other threads—remove the resistence downs. They offer no synergy other than 1 comp, which people have been complaining about for almost 2 years. Get rid of them.