I'll be punctual: Werewolf's "Terrified" effect should give some benefit for non-werewolves, and the effect should continue to be exclusively sourced from Werewolf's toolkit.
What I mean by this is that — rather than make Piercing Howl and its morphs deal 10% more damage to an enemy who has been marked as Terrified — instead the Terrified effect would make an enemy take 10% more damage from any skill.
After Subclassing broke down skill exclusivity, there's nothing stopping any player from sourcing any buff their group wants. Yet, Werewolf skills are still exclusive to those who are transformed, and non-Werewolf skills cannot be used while transformed — meaning there is still some semblance of skill exclusivity in this game. Unfortunately, Werewolf's only unique effect — Terrified — can only be made use of by players who are also in Werewolf form.
As a result, nobody really needs a Werewolf in their group — unless the group has werewolves using Deafening Roar. All of Werewolf's buffs and debuffs that a human can make use of can be sourced from sets and human form skills. There's no benefit to restricting yourself with the Werewolf skill bar if it doesn't bring anything unique to the group.
However, if humans could make use of the Terrified effect (and, importantly, couldn't source it themselves from a future set or skill) then there would always be some reason to have at least one Werewolf player in your group, be it PvE or PvP.
PC/NA — Lone Werewolf, the EP Templar Khajiit Werewolf
Werewolf Should be Allowed to Sneak
Please give us Werewolf
Skill Styles (for customizing our fur color),
Grimoires/Scribing skills (to fill in the holes in our builds), and
Companions (to transform with).