Oh Karkat. Oh Karkat how you need a hug very badly. Also not literally carrying the universe on your shoulders would probably be good.
The fact that most of the doomed Aradiabots came back in time to stop Karkat from doing stupid things is... Yeah. It sort of explains why there were so many of them, and I have actually been wondering about that. Dave only went back in time to stop a doomed timeline from happening once, but Aradia did it hundreds of times, so there must have been lots of mess-ups. Poor Karkat. On the other hand, I'm thinking perhaps that's how this game usually goes? The Time player's role is to stop mishaps from happening, and in the process get themselves killed over and over again?
In other words, the Time player, being the one who gets to see the whole timeline and knows how it's supposed to go, would be the one ultimately responsible for things happening the right way. Meaning that if this is indeed a mess-up, then it's not only Karkat's fault, but also Aradia's?
In any case, seeing as the kids' Earth is obviously not our Earth, it's not all that surprising that their universe was cancerous. Which also explains why there was a Tumor in the middle of their Battlefield, I guess.
And! This update is obviously Karkat before Vriska is killed and Karkat talks to John about the thing they're doing to try to survive. Which means that even if this was always technically a doomed timeline, and even if Karkat sounds like he's giving up hope now, he must get it back later. Time doesn't really work out in the Furthest Ring anyway, and going there to blow up the Green Sun is cheating in the first place, so perhaps they can cheat in more ways than one? (Bring back dead trolls y/y?)
And then there's the Fourth Wall. Remember that Karkat told Jade (relaying a message from Future Jade) to sketch the Fourth Wall to her Sylladex? If anything is cheating, the Fourth Wall is cheating. Who cares about doomed timelines and cancerous universes? >:D
This is also obviously before Karkat deals with Gamzee, although speaking of that...
The thing is, Karkat can't have killed Gamzee. Because there are
these two pages, in which "The most important character in Homestuck fondly regards the miracle of a new beginning. " In other words, Gamzee is there, apparently alive and at a computer when the Critical Event happens. So - what did Karkat do?
Unrelatedly, I've found where we first hear from "fedorafreak".
It's here. In which he is sort of panicking about a meteor striking his neighbor's house. Except perhaps he misinterpreted it? Perhaps what really happened was that his own house was moved to a fiery place in the Medium right before the meteor would have struck the neighborhood? (I love foreshadowing, and the fact that this random Serious Business guy apparently died on a Quest Bed somewhere is very intriguing.)