Instead of having Vicious Lacerations acting as a stacking buff, change it to a stacking debuff which increased the damage taken. Then, if you switch targets, the stacks on the first target disappear and it starts stacking on the new target.
On the one hand, it aids killing big targets in group content, but on the other hand, its worse on killing smaller, numerous enemies, as they don’t keep the damage stacks as long.
Gives Rev another unique trait to bring to raids (on top of Assassin’s Presence) and makes Ferocious Strikes better for smaller scrappier fights where its hard to keep stacks on a single target.