It's mostly ML Peerless where Disco is at 10% effectivity, the rest works fine IIRC. I remember I heard somewhere that everything with barding difficulty 160 only gets a part of the debuff, but I can't find where I read that.
But even then, a boss with 100k HP loses 1/40 (~2 each) of it's resists and skills, that's like a few K instant damage, if you calculate it like that. Multiplied for every additional source of damage, not that hot if it's only your pet doing damage. If you run a team and do damage yourself, you really bring the hammer down.
The thing is, your pet can only disco once and when it sticks, there's no further drain on the mana, so it complements other options pretty well, it scales with enemy tank and outgoing damage. No other pet skill can do that.
Of course, if your tamer runs disco themselves, there's no need for that.
Edit: Actually, Mortal Strike scales, too, though in a different way. But that would be a skill with fantastic synergy.
I guess I should try it on something first before scrolling a pet up.
