Eternity's cost is 6 
|5 which is not very high for what it offers. It deals 4 damage and it's effect ability costs 3 for a single RT per turn, while Reverse Time/Rewind cost 2 /1 + 1 card. However, if you consider Eternity as a card that can give you infinite RTs in a game while original RT is used only once, Eternity's ability should be at least 1 quantum higher than RT. However, I find RT & Rewind OP and they should cost 3 |2 instead of 2 |1 , so Eternity's ability should cost 4 instead of 3 , even if we have to reduce its playing cost from 6 |5 to 5 |4 or 4 |3 .
I wasn't talking only about stall 
/ duo decks, but also for / Shrieker rush with Eternity (or Rewinds) and Quicksands. Would you deny it is one of the most powerful rushes (if not THE most powerful rush) in Elements?
Discord is also OP and thank god they nerfed, though very slighly, its quanta scrambling, but I would agree it needs a little more nerf. Arsenic is not as powerful as most people think, other ways of player poisoning are more effective (Cryasora, Momentumed scorpions) and unupped Arsenic is easily blocked with shields of DR 2 or more. Fahrenheit is broken when you gain 75 
quanta and the truth is that the element has too many quanta gaining cards and it becomes too powerful with a lot of quanta, so I will agree with you here. Titan is broken only if combined with Flying Weapon and again only if launched via Catapult/Trebuchet or Gravity Pulled/Forced. Vampire Dagger is ok as it is, or maybe not (a slight damage decrease by 1 in both upped & unupped versions may be needed here). Eternity is IMO the most broken of the weapons. Pulvenizer is only OP in / 
duos. Owl's Eye|Eagle's Eye is ok as it is IMO. Lobotomizer is fine, Morning Star|Morning Glory is slighly broken, since it deals a nice 7|8 damage and it is immortal at the same time (painful, especially when it flies). Jade Staff can be strong when flying, but otherwise it is an ok weapon. Trident is NOT as bad as many people think, yes its ability is useful only in / 
combos but in these combos it has a permanent Earthquake/Quicksand effect, which is a game ender versus many decks if used soon enough.
1) I disagree. 6
is a fair cost for what Eternity offers.
2) 4 damage is very low, which contributes to Eternity's balanced-ness.
3) The point of playing Eternity is to be able to rewind multiple times (and gain card advantage over stuffing the deck with RTs). Upping the cost to 4
is ridiculous, and is nowhere near the power of other abilities that cost 4 in-element (antimatter, nymph creation, etc.).
4) I do not think that RT should be nerfed to 3
/2
. This seems to be the crux of my disagreement with you. RT is similar to lightning, except that RT is better against high-quanta, buffed or nova-powered creatures while Lightning is better against midrange attackers (GotP being a perfect example). Compare RT to Lightning and hopefully you will see where I am coming from.
5) Yes, I would deny that. Shrieker rush is a decent rush but by no means one of the most powerful ones in Elements, especially if you add RTs. EQs help the deck a lot, but then it's not really a shrieker rush any longer and it certainly can't have RTs and EQs. Putting an Eternity into a shrieker rush deck would be a horrible mistake.
6) Disco is very very powerful in the current meta, perhaps even OP.
7) Arsenic is very powerful against a stall-y meta when combined with other stallbreakers. Chrysaora and momentum'd scorpions are weak to CC and require duos at a bare minimum.
8- Fahren is not broken. Fire has two quanta gaining cards, same as the rest of the elements: burning pillar and fire pendulum. It also has Fire Bolt and Fahrenheit which scale with quanta. Fahren is quite powerful but remember that getting to that power level requires you to generate tons of fire quanta and use little to none. This balances the top-damage of Fahren (19 IIRC).
9) Catatitans is an OK strategy, but nowhere near OP. I'd put it on about the same level as adrenastaves - nice but not a gamechanger like antabow or monolight.
10) Earth/Gravy duos are not OP. Not even close. I do not understand how you would come up with this conclusion.
11) Morning Star is UP. Its immortality would serve it better if it did more damage.
12) Yes, Trident is as bad as most people think. 6xEQ will usually serve a deck much better than Trident, because Trident contains a multitude of flaws. Before anything else, it requires a duo. Then Trident also cannot activate on the turn that it is played. In that turn and in any turn after that it is extremely vulnerable to PC. And, unlike Eternity or Lobo or Pulvy, there is rarely a need for more than 6 earthquakes in a deck.
