...individually. It's as a whole that they are enough to scare the likes of Sargeras and scour worlds.
This is an idea I've had in my head almost as soon as the Void Lords were mentioned back in Chronicles vol.1, I've seen it suggested here and there since then, and with patch 7.2 and 7.2.5, I've seen more and more evidence to support this idea.
In the Broken Shore region, we've got mobs called Shackled Voidlord and Warped Voidlord. In Chromie's scenario, one of the creatures we fight is called a Void Gargantuan, and afterwards Chromie mentions that she 'never expected to be on the bad side of a VOID LORD, of all things'.
This is in addition to past instances of void-related creatures referred to as 'void lords' in some capacity.
These are all creatures that can be destroyed relatively easily by mortals, yet we're led to believe that the Void Lords have orchestrated the creation of the Old Gods and their attacks upon the material universe, as well as manifesting beings like Dimensius the All-Devouring, who has destroyed entire worlds.
My theory is this: Void Lords are, individually, not especially powerful. It's only when they work collectively that they are capable of becoming a world-destroying threat. We don't know what exactly was involved in the creation of the Old Gods - it may have taken hundreds, even thousands of Void Lords working together to create a single Old God. It may take many Void Lords generating a collective manifestation to create a being like Dimensius.
This could mean that the numbers of the Void Lords are in fact vast, but one on one they aren't any great shakes, and only in groups do they become truly dangerous. Personally, I think this would be an interesting take on a major threat - rather than having powerful, singular figures like Sargeras, Deathwing, or the individual Old Gods, the Void Lords are a vast, faceless mass of malevolent beings, a collective or hive of enemies, instead of a single personality.
Almost like a dark mirror of the player base.