It's common for killers who want to slow down the game running the same few perks to do so. Therefore, to add more variety in the meta here are some buff suggestions to underused perks:

Call of Brine: 

Return its regression to 200% (from a while ago) but reduce its duration to 45 seconds. At maximum, a generator would lose 11.25 charges per instance. This would reward killers for pressuring survivors off gens without providing as much regression as perks with more strict requirements like hooking or downing survivors.

Dying Light:

Each time any survivor is hooked, gain 1 token. Survivors still receive a 3% penalty to repairing, healing, and sabotaging but the obsession is affected as well. The obsession is no longer given unhooking and healing buffs. This change would discourage killers from avoiding chase with the obsession and prioritize hooks above all else. This would be a great choice for killers who want slowdown on both gens and heals all in one perk.

Eruption:

The intention of eruption is to allow killers hook a survivor after downing them without the affected generators being completed. To achieve this more consistently, the regression should be increased from 10% to 13%. This small buff should encourage higher usage.

Hex Ruin:

Similar to call of brine, ruin is a perk that rewards killers for applying pressure well. Unfortunately, because 100% regression speed is so little it is very common for survivors to ignore the totem. By increasing the regression to 150%, survivors will see this perk as more of a threat if not cleansed. (A generator at 99.99% would still take 4 minutes to regress to 0 at this speed.)

Oppression:

The design of this perk is pretty good as it is, so a few small buffs should make it more appealing. Two effective changes are to reduce the cooldown to 60 seconds and cause all affected generators to regress at 125% of normal regression speed.

Overcharge:

This perk seems to have been designed to discourage gen tapping. Since a recent update removed this, it's probably best to give this perk a complete rework.

Scourge Hook: Gift of Pain:

In order to make this perk more appealing, we need to make the slowdown affect more than one person. New effect: Upon being unhooked, all other survivors receive a 16% repair and healing penalty for 90 seconds. The first effect of the unhooked survivor receiving hemorrhage and mangled would remain.

Thanatophobia:

Because injuring a single survivor is relatively easy, one stack of this perk shouldn't do too much. Therefore my proposal is that if one survivor is injured, dying, or hooked this grants a 2% action penalty with a 5% penalty for each additional. (17% at all four)