Okay let's take this point by point.
- If you want to hit an important target with 2 encounters worth of saved aura points, you're gonna have to do it in encounter 3.
Not quite getting what you are saying here.
In encounter one, the heroic Warlord manages to curse every foe (with the feats and items available) by throwing out two curses per round. If he does not bloody any of those foes, but does curse them before they get bloodied each and re-curses them before they die, then he gets exactly 10 aura points (5 foes, 2 points per foe, one for bloodied, one for dead).
I assume that the Warlock himself (being a ranged Striker who can attack any wounded but not bloodied foe on the board) will bloody two foes with his rod per encounter. So, a total of 12 aura points at the end of encounter one. This might be more, this might be less. It could be quite a few more if minions occur in encounter one or two.
It might be less than 12 aura points in encounter one, but then again, he gets to add more aura points in encounter two. The likelihood of him getting attacked so that he uses up all of his aura points in round one of encounter two is fairly slim. Even if he does get attacked, he might not use up the aura points right away, waiting to get a few more in the tank.
So, 12D6 or 15D6 or even 20D6 sometime during mid to late encounter two is not unheard of. Yes, it is one nova per two encounters, but that's still not that bad. This is without him using a single other ability or power and it occurs outside of his turn.
This does not require two encounters of not taking a short rest and doing it on encounter three, only one encounter without a short rest and doing it sometime during encounter two.
If a bloodied foe attacks him mid to late encounter one, he could most of the time outright kill the guy and totally negate the damage on himself (and possibly others) from one attack. Not exactly weaksauce. In this case, instead of the warlock being damaged, the foe is dead for attacking him. If nobody attacks him during mid to late encounter one, it could be a win win for the warlock since he can set up for encounter number two. Ditto for encounter three / four, encounter five / six, etc.
- If one at-level MM3 standard attacks the Warlock once every round in a five round combat, the Warlock can expect to lose 75%-60% of their hitpoints. Obviously this is a gross generalization- I assume a 50% hit rate, and ignoring things like competent Defenders, enemy focus-fire, and the Warlock's inability to use Darkspiral to discourage attackers- but it gives us a ballpark idea of incoming damage per encounter.
The Warlock is a PC like all other PCs. He will tend to stay in the back and get hit sometimes and not hit other times and that's why he has healing surges, concealment, ranged attacks, etc. I really do not understand the point of your comment here.
He does not need to take a short rest in order to get healed if he does get hit.
And if the DM refuses to attack him because of the aura, that typically means that the DM is attacking harder targets instead.
- Darkspiral Aura doesn't scale at all. By level 10, 12d6 is unlikely to even bloody a standard. Even then, at L10 a Dark Pact Warlock will need to spend an AP to finish off a bloodied standard.
DA does scale, it just does not scale well. 1D6 at level 1 through 10, 1D8 at levels 11 through 20, 1D10 at levels 21 through 30.
And it will be fairly standard for a Dark Pact Warlock to take Improved Darkspiral Aura. So, 1D10 at levels 11 through 20, 1D12 at levels 21 through 30.
Sure, at higher levels, it's not great for damage. But, even at level 30, 12D12 is 78 points of damage. Not crushing when standard foes have 200 to 300 hit points role dependent and most cannot resist this damage, but still a solid outside of turn hit. Obviously not as strong as level 4, but still a solid hit, especially when one considers the weakened factor.
- A good Striker should be able to kill a standard monster alone in 3-4 rounds using only at-will powers, and be able to do the same in 1 round using encounter powers and/or an AP. In the very unlikely event that a Warlock managed to build up a 12d6 Aura every other encounter, what you'd have is a Striker which, every 2 or 3 encounters, can fulfill its role as a Striker. And even then it only works between levels 4 (when you can get the combo running) and 10 (when the damage stops being worth the effort).
But, Warlocks are not good strikers. They are controllers with a little bit of striker (or maybe strikers with a little controller). Anymore, some Defenders can do more damage than a Warlock. For pure overall damage, they are the weakest striker out there. And actually, at level 11 with IDA, a striker could still do 12+D10 in encounter two. 66 points of auto-hit damage with a weaken component against same level foes at level 11 will typically bloody the foe or outright kill a bloodied standard attacker.
This isn't necessarily a great ability, but then again, here at LEB, no PCs have even gotten to mid-Paragon yet. It's not that terrible at mid-Heroic to mid-Paragon.