A couple of patches ago (issue 12 i think?) the voids got nerfed due to VEATS having no special enemy class doing extra damage against them.
At the low levels kheldians dont have many tools at their disposal to 1) Defend themselves against high burst damage and 2) To destroy/control the void quickly.
Once you get past the teens though you'll find your resis are higher, you have access to mire/build up, a heal if your a PB, a hold if your a WS plus also remember the higher damage your going to have now from slots/nova form.
By the time your kheldian is 30+, a void/quant should be dead before the first 5 seconds (regardless of whether you see it or not) and your health bar not go down. IMO i think the design was to have voids/quants to trouble the low levels and the cysts to trouble the higher levels (lets face it, they trouble everyone really on a full team).
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It's nothing but negative energy damage so you can resist it now (it used to be special). They're only a danger at low levels because you have very little resist, and depending on your Kheldian no hard control or self heal, and just to really dump on your parade, they cause knockdown so you can't fight back.
Even so, Quantums can still be dealt with easily enough because they're normal squishy scumbags you can fly up to and unload all your most vicious attacks before they fire off more than one shot if they're lucky. Voids have effective energy resists though, so at low levels you have to dump inspirations all over them and hope you have a good day.
This is all moot if you're in a team, they can mash up Voids and Quants effortlessly. The only problem is playing solo, where Voids go strangely in the space of a single level from "doom brigade" to "mook brigade". And they probably wouldn't even be that much of a solo problem if they were actually included in the mob spawn calculation in the pre-20 levels, so you don't have a whole group of normal enemies to make it worse.
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Alright, thanks for clearing that up guys! 
It does seem that the 'special damage' has been altered into negative energy, but it still seems that the knockback and stun only applies to Kheldians
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Odd they didn't add a special enemy for VEATs you'd have thought some kind of Longbow doing special damage to them would have been obvious. It's not like your "normal" villain would come across such an enemy as they're not after "normal" villains.
It would also have ben amusing for an NPC Fortuna etc to say "Did you hear XXXXX was taken ot by a YYYYY" 
A couple of reasons why VEATs didn't get special mobs:
1) VEATs are basically normal humans (for the most part). If longbow had a weapon that did special damage to VEATs it should do special damage to practically everyone else as well. And when everyone is special, no one is special.
2) They realised that kryptonite mobs didn't work as a balancing instrument. Hence the nerfage of voids and Qs.
3) It would have delayed the realse of VEATs by at least another issue while the special mob code was added.
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Oh how I hate to when I can't find a hole in someone logic 
Im curious:
At lower levels, a void/quant can 2-shot a kheldian (IE. A PB or WS). But at higher level, kheld's seem to be able to sit there and have a fight with 'em like they're any other enemy. Why is this? I thought that voids/quants do a special kind of damage to them, and therefore giving them their weakness. Surely the damage isn't just negative energy... Is it?