Irrelevant. There are tons of Tau "first faction" players that still believe their faction matters, so it's not like "first faction" makes you more knowledgeable on the subject.
Reported for comparing me to a Tau player
After a certain point it's a snowball effect. Flayed ones and lack of agreement don't exactly matter that much because Flayed ones want to murderboner everyone as much, if not more, and nearly all of Necron lords can agree on hating other races more.
3rd edition Necrons awakening was instant game over. The entirety of the Necron race was united, the C'Tan were whole and in a loose alliance with one another against every other faction in 40k and to top it all off the void dragon would have instantly halved the Imperium, turning that half into the most technologically advanced anti-warp Empire in the galaxy. Flayed ones were regular insane and weren't contagious, pariahs were the sign of a much more foreboding plan the Deceiver had for humanity (signalling that the Necrons were going to awaken during humanity's existence), and there was no knowing what kind of cards they had up their sleeve were, like the Cadian pylons. The Blackstone Fortresses were getting offed one by one, with Necron ships helping, and a Necron scouting fleet landing on Mars itself.
Post 5th ed Newcrons severely downgraded the threat posed by the Crons. They're still capable of separating the immaterium and real space, they're still capable of potentially exterminating the galaxy, but they are nowhere near the instant-death they were when they first started.
Starting with C'Tan getting pokemon'd, when they were introduced the C'Tan were the material counterparts to the big 4 and the Emperor. The big 4 were the masters of the Immaterium, Emperor a jack of all trades, the C'Tan were the big 4 of real space. The C'Tan had absolute mastery of the material world just as the big 4 of chaos mastered the Immaterium, hence their ambition to seal the entirety of the warp away and ensure they couldn't be killed. As they could only be killed by the warp, starvation or the memestone fortresses, the C'Tan not only posed a threat to all living things in the material galaxy, they had succeeded in devouring the galaxy against stronger foes before - against the Old Ones, their gods, the Eldar's gods, against other C'Tan, and all the Old One's progeny at the height of their existence. Nothing could stop them except their own appetite outpacing the sheer scale of death caused by the birth of demonic entities & the general depopulation caused by the Necrons.
In newcron fluff, they're nowhere near the threat to humanity as they once were. The C'Tan are fragments of their former selves about as threatening as an avatar of Khaine, or a bundle of lasguns stapled together. For starters, they actually managed to get killed by their own slaves. In the old fluff even at their weakest this could never have happened, in the new fluff the Necrons have managed to split them into little fragments to use as batteries, with one C'Tan being straight up
killed by a single Necron Empire. To make matters better for humanity, the Newcrons have a vested interest in ensuring that the C'Tan shards never reunite, because the C'Tan are now the Necron's greatest enemy. A C'Tan that managed to reform into a whole God would now be fighting against every warp-aligned faction (the Imperium, Chaos, Eldar, Dark Eldar, Orks would tag along just to get a good fight) AND the Necrons, who have material-based means to break C'Tan down. The C'Tan would be contested in real space whilst having all the disadvantages of fighting in a completely warp-ravaged post-Cadia galaxy.
Of the Necrons themselves, they're no longer THE Necrons. They're a smorgasbord of unled, unclaimed tomb worlds, and a bunch of independent Empires. There is no unity of command, there is no unity of purpose, there is not even a common solidarity against the other races. Far from being a dormant undiscovered threat only the Eldar remember of, it's now a fractured mess with uncounted scores of Necron tomb worlds lost to malfunction (wat), infighting, Eldar attacks, Imperial attacks, even Tyranid attacks (in the old lore the Tyranids went around Necron tomb worlds. In the new lore the Tyranids eat their tomb worlds anyways). This leads to things like Tomb Worlds sending off invasion forces into suns and black holes where they are destroyed, or Tomb World maintenance protocols going rogue and sending necron armies to invade other necron tomb worlds to add to its mindless mission. Leaderless Tomb Worlds or ones led by senile Overlords do bugger all until a sane Phaeron shows up, and the Phaerons are all scheming against one another, or in a state of eternal melancholy at the mistake they made in giving up their flesh and bone. Far being the non-negotiable terminators of old, the new Necron leaders show a great deal of tolerance not just for humanity, but even for Eldar. Sometimes they don't exterminate an entire planet of life, sometimes they let their enemies
surrender in a
completely non-grimdark way, letting them leave in peace, sometimes they even ally with Imperial forces. Even if we disregarded Ultramarines tearing through Necrons & C'Tan alike like butter as a plot-related anomaly, the Necrons as a whole are so fractured, aimless and broken that they're barely capable of standing up against the unified elements of the Imperium, Chaos or the Tyranids. Even the Orks are more unified than them. THE ORKS. The Phaerons/Crypteks will never stop playing CK2 against one another long enough to unite under a future King, short of a temporary alliance to fuck up a united C'Tan. Some hate the youngling races, some don't mind the honourable ones, some only hate Orks, some hate other Phaerons/Crypteks more than the younglings, some hate C'Tan the most, some like Trollzyn are self-serving, some like Assholetep the Stormlord let enemies walk away from their defeat... They're a lot more reasonable compared to the non-negotiable murder bots they used to be, with a lot more exploitable flaws.
Now they have psychological flaws too. Because now the greatest Necron leaders, what they hate the most is... Necrons. Imagine that: Necrons win, but want nothing more than to see their people live again, and stop being Necrons. There's a possibility of accommodation there.
I'm not even going to bother with the flayers, a plague which reduces your already mindless species into an even more mindless uncontrollable species is going to harm unity. But I will say a game where Imperial assassins have to assassinate a target that may or may not be the Deceiver surrounded by deathmarks, pariahs, flayers and wraiths would be fucking ace
Ah yes, because they'd finish off only the Necrons.
I honestly believe the Necrons would win even harder in a second war against the C'Tan given the new lore, my point is that they've gone from being fighting on the same side, to being crabs in a bucket holding each other down. Necrons no longer want to see C'Tan win, C'Tan no longer want to see Necrons win. Both have the power to righteously fuck each other up, which gives the other races serious counterweight, against two already divided races.
Victory by suicide bombing is still a victory, although it's questionable what would even ultimately happen with Ynnead being a thing, but still, it probably either "wins" it for Eldar or allows someone else than Necrons to win, presumably Tyranids or something.
Probably squats Slaanesh to make 40k kid-friendly
while the Dark Eldar's continued relevance
Their what?
Masters of the webway, Dark Eldar unrestricted by the low-fertility rate of the Eldar, united front against other factions in spite of their internal issues. But it's really just the fact that they are webway-based which makes them relevant imo. They are the gorilla warfare copypasta of 40k, they can strike you from anywhere
If Necrons fail that still leaves someone else to win. My point wasn't "Necrons are going to win hurr" but rather that someone is, and it's highly unlikely said victory would include at least half (if any) the other races in the post-victory Galaxy.
The likelihood of everyone's end games fucking each other up to ensure no absolute victory is pretty damn high
Nobody said GW has any fucking idea what they're doing with their stuff anymore. See - Age of Sigmar. There was no conclusion to arrive, because the conclusion was "up to you". It's a sort of side-effect of the "selective canon" GW has been doing for longest while, where "everything is canon, but not everything is true". You can believe in specific faction "propaganda" and think they're the ones that are bound to win, but everyone has about the same level of legitimacy to that claim.
Sorta hard to say that C'Tan sharding is just propaganda when the C'Tan have been split into shards though
With resolution, it's not like that anymore. There is now clear answer to "who is better". It's like one of those dumb comic book "Batman vs Superman" or so, but instead this time Batman kills Superman for good, and there will never, ever, be anything related to Superman past this point (I know this is essentially impossible considering how that industry works, but bear with me). Everyone is just left with distaste. Cadia should be left where it was, and the gears should have never been turned, because there were none in first place.
Good fucking Lord, the last thing I want is 40k to become another capeshit where Bigboi 1 fights Bigboi 2 and they keep doing it again and again and again. Kill superman. The repetitiveness of capeshit is a poison, not a recipe. How many failbaddons would you take before you got bored? 14? 20? 35? 50? Turn the gears, kill Uncle Ben, stop suspending the movement of time just to keep a million allusions from seeing the light of conclusion. Lest we be stuck with an eternal Cypher of "yeah probs" that spent years building up to...
Nothing