To be fair to SB: The C'tan in earlier showings were often hilariously inconsistent, and many older depictions from the 90s or early 2000s would usually only show them as Tier 4 or so.
To be fair to the C'tan: A lot of the 40k god tier downplay over there is absolutely ludicrous.
Let's show off some stuff from
Mechanicum, which not only fleshes out some things about the C'tan, but also very recent + part of the Horus Heresy series.
- A Shard of the Void Dragon (aka The Dragon of Mars) creates a space from its memories that is higher-dimensional to such a degree that all conventional notions of direction or time become completely and utterly meaningless. This shuts down the completely laughable "the C'tan do not possess higher-dimensional power/power beyond a regular 4-D space-time continuum". This is what happens when someone experiences it.
"
She was trapped in the darkness. She tried to wake, but there was only the utter, unbreakable darkness in all directions. In truth, she could not even think in terms of directions, for this space appeared to be dimensionless. She had no sensation of up or down and no sense of the passage of time. Had she been here for long? She couldn't remember. She couldn't remember much of anything.
Her memories were hazy. She had once roamed freely, she remembered that much, feeding, birthing, and extinguishing stars without heed, but now...
Now there was only the eternal darkness of death.
No, not death, but was it sleep? Or was it imprisonment?
She didn't know.
All she knew was that if this was not death, it might as well be for all the power left to her.
Were these memories or hallucinations?
She perceived herself as female, but that meant nothing. What did sex matter to a being of pure energy and matter?
Her mind roamed the darkness, but whether she ventured across the span of galaxies or travelled only millimetres, she couldn't tell. Did she journey for mere moments or the lifespan of a universe?
Many of the dimensions she was thinking in were meaningless to her, yet she sensed that they were all equally ludicrous in this darkness."
- Dalia just barely gets an idea of the scale of this fragment of a true C'tan.
"
Dalia. That was her name. She was a human being... not a creature of unimaginable scale that defied time and the material universe with its power. Indeed, she wasn't sure if creature was a term large enough to encompass the immensity of its existence."
- The C'tan are beings of the material universe, but as we very soon learn, the hilarious notion of a 4-D continuum is one that is merely the idea of limited beings, while the true universe is much, much, much greater than that. So no, the C'tan wouldn't be "Universal" in the sense of a universe as we would describe it, but "Universal" beings of a cosmos far greater than our understanding or theories.
"'
My name,' said the adept, looking confused. 'Ah, but it's been so long since I needed one and it gets so hard to remember. I need no name, for my name is insignificant against the vast, echoing emptiness of the darkness, but men once called me Semyon'.
'
And what are you doing here?' asked Dalia.
'
Here?' cried Semyon, throwing his arms wide and spinning around like a lunatic. 'You have such a limited understanding of the material world, girl. Words like here and there have no meaning. The myriad dimensions of this material universe cannot be defined by so limited a thing as human language!' Semyon stopped with his back to Dalia and looked over his shoulder, his face alight with the fire she had seen in Jonas Milus' eyes before his body had disintegrated.
'
I am the Guardian of the Dragon!' said Semyon."
- Even this single, infinitesimally small Shard of the Void Dragon retains some of its original, higher-dimensional nature.
"
The angles were impossible, the geometry insane. Distance was irrelevant and perspective was a lie. Every rule of normality was turned upside down in an instant and the natural order of the universe was overthrown in this new, terrifying vision of distorted reality. The cavern seemed to pulse in every direction at once, compressing and contracting in unfeasible ways, moving as rock was never meant to move."
"
The monstrous horror of its very existence threatened to shatter the walls of her mind, and in desperation, Dalia looked down at her own feet in an attempt to convince herself that the laws of perspective still held true in relation to her own body. Her existence in the face of this infinite impossibility was meaningless, but she recognised that only by small victories might she hold onto her fracturing reason.
'
No,' she whispered, feeling her grip on the three-dimensionality of her surroundings slipping as the distance to her feet seemed to stretch out to infinity. Her vertigo suddenly swamped her and she dropped to her knees as her vision stretched and swelled, the interior of the cavern suddenly seeming to be as vast as the universe and as compressed as a singularity within the same instant. She felt the threads of her sanity unravelling in the face of this distorted reality, her brain unable to cope with the sensory overload it was failing to process."
But I mean, people can keep believing "star level complete C'tan" if it helps them go to sleep, at night.
To answer the actual question at the end, probably. The Necrons took advantage of the C'tan weakening themselves with constant infighting and having devoured each other. The Xeelee almost certainly could do the same, at that point.
