It looses vs an unleveled Khorne Dreadnaught (that can even get teleported if supported by a Sorcerer) *seigh*
Yeah, but... I'm pretty sure a bloodraged KDread can beat down Avatars and GUOs 1v1. At least in retail it could. So I wouldn't use the ability to beat down a KDread as a benchmark.
Orkfaeller, you're looking at the unit wrong. A VD has multiple strengths:
Improved inspiring buff
Improved HP and damage
Reliable escape
Drop pod in
If you look at what it is countered by, it's countered by Nobz, very few melee walkers, and tanks.
The advantages of it are that it is anti-all, which means that even if you get outteched by a tank, you can melta/snare/stun the tank, and drop a VD behind it, SECURING the tank kill, causing your opponent to lose 100+ power of investment right off the bat, for a 50 power 300 red investment. Then you can head for your tank straight after, giving you a solid advantage. If you had gotten a tank instead to fight the tank, there is no guarantee that you will snipe the tank, and the game might be pretty even.
So let's look at other counters to VD:
Ranged AV=> Tie it up with other units, throw VD into the mix.
Other walkers: VD will not get beaten up in short order, at worst (at best VD smacks down most other walkers). In worst case scenario, a predator would be good in the sense that it directly counters "other walkers", but it does mean that you cannot stand your ground as well if they charge your position and try to overwhelm you, and would have to kite the predator. If the predator kites, then your army has to kite, and you have to whittle away at the walker bit by bit, which is okay but at the same time a VD would be effective in a different way. I personally find that a VD+ a snaring option like lascannon is a really great way to handle them.
Melee AV=> e.g. Nobz/ Ogryns Emperor's Wrath is great, and when you try to use a normal Dread against these units you're really counting on the supporting army to force off these big units. Thus the improved inspiring buff is a big boon here, and the VD can draw aggro and tank for the army. With a predator, you'd have to rely on your knockback from your army and then kite afterwards if they are still healthy enough to charge forward. I.e. it's pretty similar to the walker case but you can use knockback.
Anyway, the way I see it is that the advantage of the VD is it can make an early and instant impact when you arrive into T3, unlike the tank. It allows you to press for a lasting T3 advantage upon impact, and retains utility if it doesn't quite result in what you want to happen. You just need to take care of it.