Comparing the current legal stats for the VoP and the Tormentor, the Tormentor was never worth the cost of 2 VoP. It has just been brought in line with their new stats.
Move 30cm, Skimmer 4+ save, DC 3 2 regenerating Shadowfields, 5+ CC, 4+ FF
2 x range 45cm MW3+ TK(1), 2 range 45cm AP5+, and a range 30cm 2BP Disrupt weapon.
move 30cm, Skimmer, 4+ save, DC 3, 2 x non regenerating shadowfields, CC 6+, FF 4+
1 x double shot range 45cm MW3+ (TK 1) FxF, 2 x 45cm AP 5+ FxF, and the Range 30cm 2BP Disrupt weapon.
move 35cm jump, 5+RA save, 4 DC, 3 regenerating shadowfields, Fearless, Walker
2 x single shot range 35cn MW 3+ TK, 3 x 45cm AP 4+/ AT 6+, CC EA +3 TK, Small arms EA +2 FF CC - 3+, FF 4+
move 35cm jump, 5+RA save, 4DC 6 x non regenerating shadowfields, Fearless, Walker
2 double (=4 shots) range 45cm MW 3+ (TK1), 3 x 45cm AP4+/AT6+, CC - 3+ with EA +3 TK(1), 2 x 30cm AA 5+, FF - 4+ with EA +2
Main differences, the shields have been doubled on the Tormentor to account for loss of regeneration. It gets 2 more 45cm MW3+ TK weapons because taking 2 x VOP would give you this for the same cost, and it has a 2 shot AA5+ 30cm mount added.
As for the VoP, many of its weapons have fixed arcs now, You can not add them to Flotillas, or take them in Formations of 2. Their CC has been reduced to a 6+. Their shields no longer regenerate. VoP have lost a fair bit for no points reduction.
All in all the differences balance the army out. You should not see more than 1 Tormentor in an army unless your opponent has a very low activation count or has min/maxed the rest of the army which means it will die/break easily and not be able to rally as well.
I have been playing DE for well over a year (quite a while before I went to Heavy Bolter last year). They were my first army in the new EA system having previously only played the second edition space marine game on the square bases. As such I have a decent amount of experience play the army. I think it is still easily beaten, by many armies. I gave examples of the Orks (specially the Feral Orks), Tau, Eldar, and Tyranids. Now I think of it, Necrons are also capable of defeating them quite well.
They are THE Glass Hammer. Hit hard, run away, hide, hug cover, assault, and are just as likely to lose the Engagement as to win it. Easily killed off standard units, more expensive, but killable WE that have less range than a lot of the other armies WE have. They have a noticeable lack of AA compared to most (except feral orks , and perhaps a few other Xenos armies) armies.
A 30cm 2 x AA 5+ is not as good as say Hydra batteries which for 150 points gives you 6 x 45cm AA 5+. They dies easier, but you can spam them, or easily attach hydras to tank and artillery companies for protection. The Titan AA is similar to the Eldar and even the Imperial ones.
Just remember those -1 to hit shadowfields just need to be hit by an AT, MW or TK weapon and they are gone - no save, just gone for good. Imperial Titans get can their shields back, Tyranid WE can regenerate their lost DC, Eldar titans get a 3+ save even in close combat against TK weapons, and only a 1 in 6 lucky crit roll removes this. Orks get more shields to account for their crummy shields. I think it all balances out.
6mm wargaming is just like 25mm wargaming with more units fitting on the same size table. Thus bigger games to get lost in and avoid the hassles of everyday living, and offerings for the dice gods.