Glad you got that out of the way

.
Now, lets start small, one God at a time:
What about Capt Piett stats for the Slaanesh daemon Knights?
How about even going further and doing something like this:
Daemon Knights (3 for 300)
Move 30 cm, Armour 4+, CC 5+, FF 4+
0-1 Castigator Cannon 30 cm 3xAP3+/AT5+
0-1 Thermal Lance 30 cm MW4+
DC 2, Fearless, Invulnerable save, Scout. Must choose one weapon or the other.
Questor (2 for 450)
Move 35 cm, Armour 5+, CC 5+, FF 3+
2x Castigator cannons 30 cm 3x AP3+/AT5+
2x Tormentor cannon 45 cm 2x AP4+/AT4+
DC 3, Fearless, Invulnerable save, reinforced armour.
Subjugator (2 for 450)
Move 35 cm, Armour 5+, CC 3+, FF 4+
2x Hellblades, MW, TK (D3), EA (+1)
2x Tormentor cannon 45 cm 2x AP4+/AT4+
DC 3, Fearless, Invulnerable save, reinforced armour
Try those and try the old stats and see what you prefer both as opponent and as player.
edit: Explanations:
- For reference, Slaanesh Titans have never had void shields except in the current Latd EA list, neither in Netepic and its past incarnations where it orginated, nor in Apocalypse version of 40k.
- Daemon Knights are currently overgunned and overvulnerable. They are always prime targets because of the danger they represent, have very little survivability or BM resilience, which makes them a poor choice for an army, excpet if you go all out and field multiple formations. The proposed stats give them much resilience, while reducing their ability, making them excellent close support fire units, hard to break (relatively) a pain due to their scout ability.
- The Questor is currently both an assault monster and a shooting nightmare, including at long range. It is however in the fluff depicted as a close fire support unit. The proposed changes reduce its assault ability and resilience (no shields), reduce its range (close support), which should make him fulfill his battlefield role more appropriately. He is very minimally upgunned (at shorter range) and its point cost is reduced to balance. Finally, the option to take singles is removed
in the context of a LatD list that allows two support options per coven, so as to limit potential abuse.
- The Subjugator is currently a an all-round poor option that has as only favourable feature its very low cost. In the fluff it is supposed to be an assault monster. Increasing its firepower and firefight ability makes it more versatile, and replacing its void shields (which are useless in CC) with invulnerable save should help it in cc against other war machines. Given its increased ability, it can now be priced at the same level as the Questor.
Questor - all you've done is remove shields and reduce range. I've never seen it dominate as a FF unit due to its strategy rating and support formations. Even in EC for it to be good in FF assaults it needs lots of support otherwise its still only 3 dice on 3s, can't see how that is dominating. I don't see its problem - its good at AP shooting, decent FF. Not overpowered.
Subjagator - I've seen taken more as you are getting a 225pt fast fearless WE which gets it taken even though it never gets to perform its niche of WE CC on WE. It needs no help when in CC with other WEs. Your stats make it good at everything and I can't see why you would ever not take it over the Questor.
IMO you stats make no difference to the Questors strength (AP shooting) and nerf something that wasn't a problem, the Subjagator gets help in something it already excels at (when allowed to) and made into an all-rounder.
Lack of shields is another factor, I'd suggest most armies would shoot and break them at every opportunity. That's only a feeling though as its not based on TESTING.
Knights - not seen problems with the current stats really, they are good at shooting but vulnerable (As you've said) In my experience one solves any problems with the other and they are a regular choice.