I did a lot of PTR tests, and while I never played the ES build on live servers, I did attempt to create an ES build and test it. As someone not biased by the huge damage drop, and as someone trying out the class for the first time on PTR post-nerfs, this is my honest opinion about Warlock in general:
Warlock is still an elite class, among the best for all content. It is not gutted into uselessness by the nerfs. But while I do think nerfs are healthy for the game, and live Warlock is by far overpowered, I think the nerfs they did are not good for the game. Warlock does not feel weaker, it feels worse and less logical. It has actually been destroyed in a different way.
The signature spell, Bind Demon, is overnerfed. It is no longer able to compete with basic summons from other classes. It cannot tank anything, its curse does not proc, and even with a good aura there is no one in your summon army to benefit from it. My Druid’s summoned Grizzly is a better tank than a Stoneskinned Terror zone Lister the Tormentor, and guess what , I can resummon it instantly at no cost when it gets low on health. A pure summoner Warlock will not even invest in Bind Demon because they are far better off running around with 3 Tainted, which is only good because it is broken due to a scaling bug.
To play summoner Warlock, one has to invest into the Eldritch tree to grab Mirrored Blades, put on melee weapon, and take on the role of a tank personally. That is the only way to play summoner Warlock, other than abusing the Tainted bug.
Other builds will just invest the minimum requirement and pick any random demon to act as a glorified aura stick, less useful than your own Act 2 mercenary, equally squishy or squishier, and dealing less damage.
Echoing Strike is kind of okay. If geared properly with high-end BiS items, it is even very good, comparable to or better than Hammerdin. But ES Warlock’s high health single-target damage sucks, even with Mirrored Blades.
I did not test Fire Warlock much. I do like the build because it reminds me a lot of the Sorcerer from Diablo 1. I played a lot more with the summoner build. The little bit of Fire Warlock I tried out on live servers seemed okay to me, somewhat weak against fire-immune enemies and not very efficient against bosses, so I do not think that needs to be nerfed too much if any.
I am not advocating Warlock buffs, but do not destroy its identity. Why would a Warlock who is investing 90% of his skill points into the Demon tree avoid using its two level 30 skills, Bind Demon and Consume, because they are too weak or have no use for him?
If you are about to nerf Demon, then make it resummonable so I can recast it like any Druid or Necro summon out there.
If you are afraid to give ES build reliable curse proc, why not think about what happens to summoner Warlock when his minions lose 100% damage from Amplify no longer proccing, on top of a 50% damage loss from the nerf to Sigil Lethargy?
Why not leave the damage bonus on Lethargy, but make it apply only to your summoned demons and not players?
Why not nerf curse proc for other builds, but allow summoner Warlock to scale proc chance with dedicated summoning spells like Death Mark or others, or simply give more flat damage bonus to Bind Demon or Death Trap?
Why destroy one build and the signature spell of a class just to keep in check bugged and broken builds that do not even need Demon to function properly?
I know this because I cleared P8 Hell with only two Defilers.
I am not crying because they broke my boy (even though I am a little). I still made a very powerful summoner build on PTR that is stronger than any Druid, Necro, or even Hammerdin out there,one-shotting P8 and destroying Ubers in seconds. But I did so by multiclassing into the Eldritch tree and taking the mantle of frontliner myself. I also had to abandon the Cursed Demon and find a Stoneskinned one just so it could survive as an off-tank and aura stick while I personally proc curse with Reaper’s Toll.
here is a video where it first fights Ubers and after that goes P8 chaos sanctuary, this is just prototype , surely it can be far better when optimised:
https://www.youtube.com/watch?v=1R45dRuCOfg
This is still fun and more than reliable, probably even better than it should be, but I do not think this is how it is supposed to be.