Q by dlaudghks: Superman arrives in brockton bay when leviathan hits. How does worm change?
I'll stress that I don't know enough about Superman continuity to remark too much on the Rebirth version specifically, will just assume comic version with a high baseline strength.
Standard superman could probably drive Leviathan into submission. Maybe not kill, and hurling Leviathan is harder than one might imagine with the water echo materializing matter between the grip and the giant, variably hyperdense scaled beast, but for all intents and purposes the end result is the same: the fight might go worse initially, especially if Superman tries frost breath, but Leviathan is down and out, Brockton Bay doesn't take a fraction of the damage it did in-story.
And, as happened in-story, Scion is liable to show up further into the fight. Instead of delivering a look of disgust to Eidolon, he gives a great deal of attention to Superman.
Short term consequence: Brockton Bay is saved.
Medium-term consequence: the shard network begins producing Endbringers that Superman can't stop that Eidolon could. Superman is forced to work with the top heroes to understand what's going on, there's mass panic, and things might even go more smoothly, in the medium run. Eidolon gets to be more of a hero with worthy opponents (but the power drain starts accelerating). This may lean to Eidolon being forced to tap into the real power source and start draining capes. Cue some back and forth on morality and whether it's right, even when Eidolon limits himself to taking the lives and power reserves of capes who are already dying (maybe at first when they've given consent in advance, but throw in edge cases and Superman believing he can rescue people, and ramping pressure from the new Endbringers...), cue a few Eidolon vs. Superman conflicts. Eidolon's powers give him the strength he needs to match and even beat Superman - a worthy opponent without needing an Endbringer.
I do know that Rebirth Superman supposedly heavily emphasizes family and being a leader. Being cut off from Lois and his kids while also facing a world that's in pretty dire straits may strain and test him a lot on levels that have nothing to do with super strength.
Cauldron is liable to intervene on some level, if Superman is honest about his origins, and try to tap him as a resource, but he's also a reporter and in trying to figure everything out, he might start to zero in on the fact that Cauldron is sketchy.
Jack Slash gets stomped, Siberian gets found out and stopped, the worst major players get handled.
Long term consequences: Gold Morning doesn't happen in 2013.
At the end of the day, the very reason the entities have a Warrior and a Thinker is that they exist to forestall unknown factors. In the absence of the Thinker Eden, Cauldron did arise and while their end goals are different their ultimate functionality is very similar to Eden.
Eden exists to forestall those scenarios where people might figure out what's going on, band together, and work around the problem (as happened in story, more or less). We see her doing this in the alternate history where Eden is around. She also does the finer tuning of processes and adjusting of experiment/shard-host interactions as required to manage everything.
Scion exists to handle unexpected variables along the lines of weapons the people might produce that somehow get past the thinker, shard interactions that scale beyond the test, or... aliens from another world. Yeah, Scion exists specifically to combat and manage forces like Superman. In the medium and even the long term, dropping a Superman into the picture means that Scion has a reason to exist, one that goes to his core functioning, core purpose, where the lack thereof is his biggest weakness. Superman as an unknown variable is a valuable variable, and any attempts to get home may be forestalled - Tinker makes a gate, uses Superman's signatures or whatever to key a way home, and Scion shows up to Still it.
Depending, they may ultimately fight (and a less dejected Scion with a purpose reinforced by thousands of cycles is no slouch), or Scion may employ other mechanisms, using the broader cycle. Having Superman trigger and getting into his head & biology is definitely in the cards (especially when Supes is a family man that's potentially gone months or years without his family), and Scion as a trusted force calling Superman an Endbringer or going on the hard offense vs. Superman could in itself leave Superman with very few people willing to work with him. The trigger works if Scion needs that measure of control to manage this very powerful alien that's stampeding around the broader experiment, as is drawing more on the forces of the setting, like actively using the shard network with a hand on the rudder.
But in the end, Scion wants the cycle to continue and escalate, he wants to turn Superman into a caged beast that can contribute to the experiment, and he's equipped pretty much as a guard/management feature against superman isekais, with a fair few tools to handle even someone as strong as Superman. Invincibility penetrating shots (if he even deigns to shoot and doesn't just radiate that damaging influence in every direction, disintegrating any cover), back-end tools with the shard network, ability to step into other dimensions.
So Gold Morning doesn't happen because Scion doesn't throw a tantrum. His lack of motivation and vulnerable, undeveloped humanity are his biggest weaknesses and the introduction of Superman to the setting counteracts those. Scion as an Eden-less entity as a mirror to a family-less Superman should get the input and reference points he needs to develop more as a human being and figure out how to manage being bullied to death, and having a Superman around gives him a job to do.
Even being super generous to Superman, I think it'd be unfair to give him the win vs. Scion, given what Scion is. I wouldn't say it's impossible, but it's not a test of strength. It's a test of Superman being able to come to grips with the setting, Cauldron, getting past the various obstacles and come to terms with the morally grey and political aspects of the setting (Dragon's fetus pilots, seen with X-ray vision, the PRT as a managing force). At this point, though, you run aground on the 'narratively satisfying for a superman story' part and the fact that even with all that Scion is supposed to be able to handle superman isekais, even without the thinker.
Except if it's a comic. Then there's a solid chance the writers change at the midpoint or the last leg of the story, key character elements like Scion being what he is get thrown out the window, we get a rushed resolution, something about the entities being responsible for Krypton exploding, Superman gets angry, kills Scion, goes home, vaguely unsatisfying ending.
(Fuck, I'm still so frustrated over that happening with some of my favorite comic runs.)
