Grudgeborn Fury and Oathstone both possess similar issues: they are 13 point speccable abilities, effectively the capstones of their trees as m4s are almost never taken, and yet they are both relatively lackluster, and typically outshone, in both group and solo play, by choices in Brotherhood tree.
Grudgeborn Fury is a pure damage ability, but hits rather softly despite being a 13 point channeled ability. Compared to its counterparts such as Ether Dance, T'ree Hit Combo, and now Relentless (with appropriate tactic, granted), it simply does not do enough damage to justify losing out on AAs (which are now almost always at 50% haste due to Stubborn as Stone buff, ty Torque) and other abilities during the cast time. As Penril tested in an earlier thread (the armor debuff one, if I am not mistaken? On phone, will look up later), Grudgeborn Fury was the 2nd lowest damage tank channel in the game, bettered (worsened?) only by Chosen's Relentless, which has subsequently received a (much needed) buff.
Moreover, taking this ability typically means one misses out on near-essential utility abilities such as Oathbound in Stone, or the various abilities in Brotherhood. Finally, the high base damage of Earthshatter in Brotherhood means that in a 2h build, getting Earthshatter almost always provides more on-demand burst, not to mention an aoe snare, meaning Grudgeborn Fury simply cannot compete in either damage or utility.
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1. Grudgeborn Fury -
A: Simply increase the base damage. The ability should, ideally, deal more damage than one would otherwise do while auto-attacking/using other damage abilities. The increased critical chance due to Grudge is a fine method of scaling the damage as well, but currently the base damage is simply too low, meaning the crits are not particularly intimidating.
Edit: Since replacing the crit modifier isn't a thing, I support simply raising the base damage. As Penril tested all the tank channels, he knows GBF has astonishingly low damage for a 13 point dps ability and I would assert that due to such low damage, it is completely overshadowed by other IB abilities in conjunction with auto attacks.
If this proposal gets moved to discussion, I would ask some people with better geared IBs to test how hard GBF hits now, and how hard their normal dps rotations hit in comparison. We can organize that later, and obviously I can contribute as well. I firmly believe this discussion would benefit from hard data over feels, however (especially since I am reasonably certain it would prove my point).
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Edit: I have no further suggestions for this skill. If the original idea is possible, I support that, though with a potential damage nerf, as Oathstone hits around 800 per tick at r40 and max grudges, and making that a more reliable form of damage would be pretty harsh.
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