It's actually not as bad as it seems. There seems to be some widespread misunderstanding of the difference between Ferocity increases and increases to Critical Damage.
Pure Strike, a trait from Warrior's Spellbreaker elite spec, increases Critical Damage multiplicatively to Ferocity, making it much stronger than a seemingly equivalent amount of Ferocity. So far, all direct increases to critical damage works the same way. It's very likely it'll work this way with this new trait value as well.
So, for example, if you had 200% crit damage from Ferocity without this trait before, you'd have had 230% crit damage from Ferocity with it. After the change, you will instead have (2.00 * 1.15 = 2.30) 230% crit damage. If you have more than 200% crit damage from Ferocity, this change buffs your critical damage - having 210% crit damage from Ferocity will cause the trait to grant you a total of 245% crit damage, 5% more than the old trait. If you have less than 200% crit damage from Ferocity, this change nerfs your critical damage - having 195% crit damage from Ferocity will cause the trait to grant you a total of 218.5% crit damage, 6.5% less crit damage than the old trait. So, the crit damage portion of this change will actually be a significant buff for DPS builds.
The crit chance loss is harsh. It might now be higher DPS to take Decimate Defenses to cap on Crit and lose out on Soul Eater rather than use those couple of Assassin pieces, though I doubt it. Even when using a couple Assassin pieces, however... At a glance, I believe the increased critical damage from this trait will at least make up for the loss in Power from that.