Alright, let me make headers same as you do.
ALLEGORY: HOMESTUCK IS NOT A ONE OF THOSE
Sburb being a creation myth doesn't make it allegorical. It is very much about these kids very literally creating a universe in the text. Same for coming of age: it's not an allegory about coming of age in general, it's about these very specific internet friends literally growing up over the course of these specific events.
Neither does having themes make it allegorical. Themes are, generally, about literally what happens, and how it echoes The Way Things Happen In General.
"If you read Homestuck as if it's an allegory for growing up" but it's not one of those! You literally just quoted Hussie saying it's a creation myth. A creation myth is not an allegory for growing up, those are completely different things!
"Therefore, we are not meant to read SBURB's destruction of the old world as fully literal; we are intended to read it as metaphorical." Incorrect! This is a creation myth. Things happening to universes do literally happen. This is a story of a death of two universes and creation of a third.
HS was always going to be a story about an extremely elaborate creation myth. As elaborate as I could conceive. In the HS reality, Sburb/Sgrub is the means by which universes procreate. Planets and civilizations are the seeds from which one or many new universes will blossom if the players succeed, at the expense of the life on that planet.
I always saw HS as an exploration of young people developing relationships over the internet [...] There's a lot more to HS than just that obviously,
So no, we are in fact meant to read all the deaths as literally happening. Everyone said to die very much did litearlly die. Does it have PARALLELS with regular growing up? Yes, of course. But the game takes that up to 11 in a very cruel way.
Your own analysis (as well as generally accepted analysis across the fandom) generally takes literal in-universe events seriously. Eridan has been killing from a young age, and this traumatized him. It's not a metaphor for doing something else, it's a story about a child soldier. Rose is not a metaphor for children misunderstanding their parents, she literally grew up with an alcoholic mom which fucked her up. Feferi is not a metaphor for rich kids, she's an example of one.
This is an important distinction: when something is an allegory, we aren't meant to ask questions about literally what happened. Do foxes generally eat grapes? Doesn't matter, the fox is an allegory. The story is not about foxes.
Meanwhile in most instances of "themes", we are meant to read the text literally, and find themes in that literal reading. Characters are not metaphors for something else, they play the role of themselves. They are meant to be taken literally as examples of what the work wants us to think about. Raskolnikov is not a metaphor for the economic system or whatever, he's literally a 19th century university student who got stuck in his own head a bit too much. It's a story about 19th century university students and the world they live in. It's stuffed with themes to the brim, but it's not allegorical. Raskolnikov's social class matters. Raskolnikov's living situation matters. Raskolnikov's social group matters. People Raskolnikov meets and who exactly they are and what exactly their circumstances are matters. Raskolnikov's actions matter. He goes to prison not because transgressing against society in general merits voluntary incarceration, but because he literally killed two women and it's that specific act in that specific context that he finally manages to process correctly by the end of the story.
Unlike the story with the fox, where the actual species of the fox is completely irrelevant to the story, in non-allegorical thematically rich stories every single detail matters. They are detail rich, and we are meant to take every detail seriously and understand the reasoning of the characters and the events that happen in context of that detail. The curtains were blue, and this made the mood of the person spending every day in that room a little more melancholic. Rose was left without a chance to ever talk to her mom, and turned to drinking as the last tie she has to her. The fact the kids' guardians literally died, and not just stepped back to let them live on their own, changes the calculus of what they do and how they think drastically.
Homestuck isn't just a creation myth, and it's not just a story about kids growing up. It's a story about KIDS GROWING UP IN A CREATION MYTH. They panic and flail because they are kids growing up; their mistakes have catastrophic consequences and their fears are multiversal scale because it's a creation myth. You can't just cut away one part and interpret the other part as allegorical. Just like how Homestuck is not an allegory for regular kids growing up in a normal society, Homestuck is not an allegory for competent adult creator deities making a world. Both these parts are quite real, and it's their INTERSECTION that Homestuck explores.
(Hence all the references to real life religions. They serve to drive in the point that yes, this is that epic, you are meant to be that scared and take things that seriously. The Welsh sword is in fact that significant, lighthearted jokes or not)
PREDESTINATION, FREE WILL AND CRUELTY
Indeed, Homestuck predestination runs on free will. Events happen the way they do because of a complex mathematical equation involving the personalities of everyone involved. That's why I talk about Caliborn's responsibility for what he did, instead of saying that it's not his fault because it was fated.
However, the way predestination works robs characters of the ability to make informed decisions. Dave had no way of knowing he was dooming his timeline when he prototyped Lil Cal. Karkat skipping the last frog didn't realize he was giving the new universe cancer. Jade and Jake making John a present had no idea it would enable Jack's ascension. So on and so forth.
The way predestination works bases everything on what the people involved are like, but it doesn't go for the best case scenario. As far as I can tell, the "gravity" of the alpha timeline was towards the Lord of Time's existence and powers, since that's what those powers are. Karkat goes on a whole monologue about how other versions of him god tiered (grew up! matured! confronted death!), but he personally didn't, and he's the one who gets to survive "because the alpha said so".
(Lord of Time powers given to a lonely, miserable, angry preteen-to-teen, whose idea of how to use them boiled down to an immature fantasy - this did not doom him because fantasies like this generally doom kids, they don't. It doomed him because of the out-of-his-control amplification of his immaturity by the game's mechanisms)
Even where they did have information: put simply, if you give a 2 year old a real gun, you're responsible for the resulting injuries, not the 2 year old. If you put a 7 year old behind the wheel of a stick shift car that's already moving in the middle of a busy intersection, you are responsible for the resulting damage, not the 7 year old. If you give a 16 year old a button and tell them that if they press it, everyone on Earth will die, and they don't believe you and press it to prove it, and everyone does die, that's on you for making the button and giving it to them, not on them.
And in all of the above situations, the act of giving them the responsibility they aren't remotely equipped to handle is, in fact, cruel.
And so: the 2 year old would be wise to be scared of the gun and refuse to touch it. The 7 year old would be wise to throw a tantrum and refuse to touch the steering wheel. The 16 year old would be wise to turn around and walk away, or perhaps call for a trusted adult.
So in this game, refusing to engage and striving just for escape is not an "immature" position. It's just trying to kick off the bottom and raise to the surface against a current that's trying to drown you. Even if it keeps insisting that it's for your own good.
SUMMARY
I don't have different sources than you. I don't disregard Word of God to construct my own death-of-the-author'd interpretation. I read the text as it was written, with Hussie's comments in mind. (It's been years. I've forgotten the specifics. But they shaped how I read the story, how I understand it and how I remember it. Thank you for bringing the specifics back)
And the blood is on the gears.
