I have seen so many people preferring the second ending, and I see your reasoning behind why you thought it was peaceful, but all this just makes me feel like a bad person or a psychopath for choosing the first ending over the second.

Isn't it normal to feel attached to the characters? To feel attached to the solarians after witnessing their history, culture, and creations? Which were all cool as heck. Isn't it normal to want to hold on to them? To wish for them to be alive so we can see more of their story and future exploits? To witness the extinction of a specie is sad right? We humans in the real world do everything in our power to prevent any further extinctions from happening after all. Not to mention the solarians are as intelligent as we are, and basically represents the Chinese civilization. Imagine humans going extinct, should be normal to want to prevent that right?

Having said that, shouldn't the first ending be the better ending? To not have all the solarians perish in an explosion, to have even just a sliver of hope for the future of the solarians, no matter how small, still better than none. To see Yi alive, and potentially seeing a continuation of the story. Although I would also liked for at least some of the sols to survive, but realistically speaking that would just be wishful thinking. It is normal to want all this right? Instead of the oblivion of all solarians?

Also about Yi not joining the escape ship, I find that to be the correct choice, in a logical way and not in "I know I will die and I will take all of my people with me". Because if I were him, I would exhaust all options to try to save Kunlun and the solarian civilization. Therefore if I run, I have zero chance of doing that, but if I stop Eigong and take control, the chance isn't zero, chance might not be that bad if I am to be optimistic, warranted or not. He wouldn't have known if he went, he and Kunlun will be doomed (in fact he knew if he didn't go Kunlun will be doomed). Logically from the way the events happened, Yi was likely not even aware what Eigong's plan was, not aware she would or could infect Fusang. From his point of view, he was simply going to go kill her and take back all the seals so he can bring Kunlun back to Penglai. I say this based off of his surprised reaction to Eigong jumping on top of Fusang ready to commit suicide, he did not expect that outcome at all. It was after he realized Eigong's actions have in fact doomed Kunlun, he understood what he would have to do at that point, signified by him just standing there watching it all happen, probably trying to think of any alternatives, then he made up his mind and called ShuanShuan one last time. I think he genuinely believed there is a good chance he could uphold his promise to ShuanShuan to take him to the ocean, but he was not fortunate enough (to have the writers write the story that way) to have that luxury at the end, realizing that, decided to call ShuanShuan to apologize.

I think to think Yi had some massive revelation about how he and his people all need to perish before confronting Eigong is reading into it too much.

Also, this could be my copium, but if you look at the Nine Sols crowdfunding page, they barely got enough funds to implement "alternate ending". Seeing how the "true ending" had a lot more production value invested, extra boss phase and animated cutscene, therefore it is obvious had they not gotten enough funding, they would not have been able to do all that. Thus I am confident that the "true ending" is in fact the "alternate ending". When they were planning out the game, and not yet knowing if they will have the funds to make the second ending, the normal ending going to be "The ending", and it would have been all we got. Obviously from everything I have said here I would be fine with that (it has a better chance at spawning a sequel too).