Patch 3.3

Wall of text inc...

Chains shouldn't require 19 more skill points to get to the current level imo. Chains simply shouldn't get to the current level. Ever.

Bolt is fine as is since it starts out a decent early to mid skill and then drops off a bit later on (as most lvl 1 skills do).
Abyss is also fairly solid as is, offering pretty good performance but nothing that really stand out as "overkill" compared to other solid builds.
Chains, no matter how many skill points you throw at it, should simply not do anywhere near as much dmg as it does. Either cut the max chains to 5-7 or drop the DPS by 30-50%, whichever. Yes, that is a lot but it honestly feels justified. As is, since you can now at least freely pre-cast it through your summons, chains in many situations effectively invalidates things like Abyss as you'll just stick to chaining on any Baal wave, Herald spawn, dia spawn or really anything where you can pre-cast. And if you have Enigma, even for many sturdier packs that you can't pre-cast for (drop a few chains -> tele across -> dead pack faster than Abyss would do it). Esp. on P8.

Setting aside the insanity that is "chains when they work" though, I'd actually argue that being able to combine a Chaos build with a decent bound demon is actually a pretty cool idea. It does work for both, fire and magic Chaos as their skill point invest is nearly identical (63 fire, 64 magic since you still want the sigils) and it gives you a solid caster/minion combo build with actual solid but not completely OP (again, ignoring chains) performance on both fronts. That is a fairly unique and fun thing to have and imo a definite plus for warlock design. Also something that further differentiates the trees as eldritch tends to require far more skill points, meaning they can't get a proper demon up. So basically, you get "eldritch = self-sufficient lock, Chaos = caster/minion hybrid, demon = minion focus". I'd let that stand as an overall plus and interesting differentiator in lock design/balancing.

That said, looking specifically at the demon tree, the overall performance of bind is fine atm imo and even without any Blood Boil usage it tears through P8 TZ96. And unless you exclusively stick to "no fire immunes!" zones, I honestly don't get the "terrible compared to Tainted" criticism. A proper bound demon with a couple defilers to spread the love is crazy good and on average clears many a place faster than Tainted do. At least for zones that also include fire immunes, such as CS runs, where Tainted slow down pretty hard.
I'd argue that for a full demon build, bind is now pretty close to where it should be.

Tainted by comparison are kind of in the same boat chains were in pre-patch (and still are to a far lesser extent, thanks to the target-dmg-bug still being a thing):
- They're situationally rather OP (for chains that was "when they worked and didn't get blocked", for Tainted it simply generalizes to "when target isn't immune/very highly resistant to fire").
- They're situationally pretty crap (for chains that was "whenever they didn't work or got blocked", for Tainted whenever the target is fire immune/very high res).
- Ultimately, both add up to "yeah, it evens out".
But "OP or crap" is kind of trash and un-fun binary design I dare say. So there should be fixes to remove the "crap" side of it, accompanied by balancing to tone down the OP side of it so it still ends up somewhat balanced. For chains, they now got mostly fixed (target bug still remains but less so) so should get nerfed to drop the OP side of it. And for Tainted (and any other summon for that matter), blizz really should make minus res from gear work and be inherited by all summons/minions to remove the "crap vs. immunes" side (since even Conviction on your merc doesn't help all that much when penalized) and then when doing that also nerf Tainted dmg significantly to equally tone down the OP side of it and end up somewhat balanced (other summons should still get the -res treatment but don't really need toning down to go with it, seeing how druids/necs just kinda suck across the board in that regard and still wouldn't exactly be great, even with -res working).

Though there might be something to be said for e.g. nerfing Bind Demon health (noticeably) from what it is now but in turn making Blood Oath work with it. Ideally perhaps hard points specifically so +skill gear doesn't overrule the idea behind it. Additionally, perhaps make the dmg transfer on Blood Oath more linear (-> far lower at lower levels).
A proper demon build would have Blood Oath maxed for Blood Boil and other demons anyways, meaning for them it'd be no change (or perhaps even a slight buff to make things like ubers a tad more bind-focus friendly).
A Chaos build on the other hand will still need their points in bind and at minimum 5 or 10 in mastery so they simply can't get Blood Oath anywhere near a demon build's level, meaning they'd end up with a bound demon that is still a solid choice to preserve the hybrid character but that would require a bit more babysitting than a demon build version and that also wouldn't act like a mindless absorb-shield to the same degree since the demon would not only be more fragile as already pointed out but it'd also transfer less of the dmg taken to it.
Alternatively, make the Death Mark crushing blow synergy not only work for goats but also for bound demons. Again gives demon builds something more valuable especially for ubers and comparable while leaving a Chaos hybrid short on skill points to really benefit from it.