Warlock Grimoire of Synergy "Buff" - I don't understand it

Warlocks, what am I missing here? What exactly does this buff?

Current rune tooltip:

Grimoire of Synergy
Recite from a dark tome, granting damage done by you or your summoned demon a 5% chance to increase the damage done by the other by 5% for 15 sec. Recitation lasts 30 mins.

New patch tooltip:

Grimoire of Synergy
Recite from a dark tome, granting damage done by you or your summoned demon a 5% chance to increase the damage done by the other by 25% for 15 sec. Recitation lasts 30 mins.

For PvE: The only spec I could see it buffing most would be destruction warlocks that have talent points in improved firebolt (or anyone with improved firebolt). But even then you give up 10% damage increase every time you crit. And this proc rate is 1 out of 20 swings to benefit the caster. The imp will of course do more damage too from the proc’s by the caster.

POTENTIALLY for affliction locks you could see some small damage increases if you’re lucky with procs. But it’ll add even more complexity cause we prefer to have our dots applied when this unreliable proc is up.

From a pvp perspective this is terrible. Doing some testing the 1 of 20 chance for this proc (5%) is magnified in how bad it is when you consider locks in most situations don’t use their pets to attack. For reference I tried it in duels and got a spriest down to 40% HP using only my pet and it still hadn’t proc’ed.

So what am I missing? How is this unreliable ability a buff for locks? Seems only worthwhile leveling with a void out to me. I think the other runes are still better. Maybe I’m missing something.

My big question for the dev team: What was your targeted buff spec/mode of gameplay?

Yeah, proc chance is still pretty low, but when it does it shines through. Have to remember it also works for your pet on each of your casts. Also, think of it more like one of those chance on cast to proc X extra AP/SP.

Right I could imagine some slight pve increases in damage mainly due to pet damage increases. Ironically I think it benefits destro most which is already crushing it. I could be wrong though…

What is the name of the buff you get when it procs? I want to make a weak aura.

edit: nm found it. Has the same name as the standard buff “Grimoire of Synergy” but has spell ID 426303 instead of 426301