You are comparing a one off spell with a repeatable effect. Compare Purple Nymph here.
Also because the cost is spread over two effects iots faster. I only need 5 light to play on the opening turn and can be doing damage whereas Antimatter spell requires a target and is dead otherwise. The Purple Nymph requires 9 entropy and then 4 to activate and is weaker to removal than Zenith.
Moot point because we now know that it can't reduce attack below zero.
Because its better fractal'd. Using 2 or 3 Nadir to kill any creature your opponent plays and having 5 damage for 5 is awesome. I Get my creature and my creature control in the one package.
If you start using fractal on it, then it's a two card combo AND you need EIGHT quanta of a different element and a spell that drains all quanta of that element when used. So I think comparing it to a two card combo that can be used in-element and costs six TOTAL quanta of one element is fine.
Hence, I would rather have 2 or 3 eagle eyes killing any creature the opponent plays and having 7 damage for 5 is awesome.
And if you go on saying that you can play more than 2-3 nadir, sure you can, but then you won't have the quanta to use the ability. Think fractal chargers. You rarely have enough quanta to play more than 1 per turn, so paying 4 darkness to pay for two nadirs ability basically uses all the dark quanta you're making.
Using one at a time on a tougher creature is redundant. In combination with other Nadir, parasite, otyugh, mutation, you can easily strip larger creatures, just as you would with any other creature control. Gaining 3 damage on a creature is worse than removing an opponents creature. What are darkness's better ways of creature control than nadir?
Zenith and Gravity shield and Otyugh. What else do I need? I would say Gravity pull, but BS changed details to now remove the immunity to damage just today.
Um, so if we're including other creatures too, can I just say that in combination with eagle eye, parasite, otyugh, mutation, maxwell's demon, and fire/death/whatever nymphs you can easily strip larger creatures?
"Just as you would with any other creature control" is the key here. Nadir is just another form of "any other creature contol." It is by no means better than the present ways of dealing with creatures. You show me a deck that uses Nadir's to OPness, and we'll talk.
Siphon life is better, and vampires allow you to not HAVE to remove creatures since they heal you.
By that logic, Otyugh Earth Nymph and Gravity Shield. What else do I need? Otyugh Grav Shield and Heavy Armor. What else do I need? Or, for the immortal factor, Quinted Oty Grav Shield and Lightning. What else do I need?
Zenith + Grav Shield + Oty would be nowhere near OP.
You don't need random permanents tho either. Any permanents you do have likely include a weapon like Titan or Morningstar or Discord, or a shield like Disipation. Why would you want to risk having that key item destroyed?
Well, maybe it needs a small buff, but randomly getting bone yards and empathic bonds sounds like fun to me

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Lol. Not really. Three is no greater generated effect within a single element. But when two elements overlap, the generation of quanta required for one is also generataed for the other creating a better fuel usage. You'll notice that Shrieker decks generate more time quanta than required. If you add a card that uses that fuel for an additional effect then you have achieved a synergy. This is the same concept of a Rainbow Nova deck. if you generate fuel across all elements then its better to play across all those elements to get the highest use of that fuel rather than leave it to waste.
Yes, but the problem is, if you're using both rook and ruhk, you aren't generating any extra air quanta to play the ruhk. You may create enough extra air to pay for an eagle eye, or maybe even a sky dragon, but a ruhk? Nah. So the comparison between shrieker rushes and rainbow nova decks doesn't work.
So its powerfully cheap but I lose because its too expensive. Interesting.
Yes, that's essentially the problem with the card

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-It doesn't work very well in conjunction with Rook.
-But it HAS the ability and synergy there, so it needs to cost a little more nonetheless.
Doesn't seem like good logic, but when you look at Ruhk as a standalone card, 16/8 with a nice ability and sometimes protection for 16 air is OP. Even increasing the cost by 1 would satisfy me

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And another note about rook. I don't get the "it's delayed if you have more hp than your opponent". Is it supposed to only be able to be used if you're "retreating" or something? If that's the case, then we're acting like you're sniping down on the creatures from the rook, correct? Why wouldn't I stay up there and snipe even when I have more hp than my opponent? And send my creatures down from the rook to attack? It just doesn't make sense imo.