Quintet isn’t that sci-fi either - it’s post apocalyptic but you could transplant it to any number of historical settings (such as any Gold Rush) and it’d work fine.
I mean, it is (as I understand it, correct me if I'm wrong) speculative fiction with a fictional setting and a fictional disaster and fictional game, which are based in science/science-like approaches rather than fantasy, if that's not science fiction, we're getting into very dangerous waters where we have to start "No true Scotsman"-ing a whole bunch of less extreme SF. The "you could transplant it to another setting and remove the SF elements and tell basically the same story" thing is true of like, a huge amount of SF, not like, oh I don't know, Star Wars and maybe the majority of episodes of Star Trek.
Whereas it is fair to say Capricorn One isn't sci-fi, because, well, there's no science-fiction, it's just a paranoid conspiracy thriller. I think it fits into the same vibe as a lot of this and appeals to the same people/interests so it's fine to include it with them though.
Phase IV only goes full SF at the end, of which there are at least two versions, one more grounded and one wildly fantastic.
Oh my god that explains why I was really confused the second time I watched it because the ending was way less cool than I remembered but I didn't remember specifics. I must have seen the grounded version the second time!
I'd replace it with Space Battleship Yamato.
Come on, you can't take Silent Running off and then just put that on, because frankly, way more people know Space Battleship Yamato, especially people under 40, than Silent Running. Not that Silent Running is a "sleeper", you're right to say it's not, but neither is Yamato.
Not bad, but also not great. I'd replace it with Fantastic Planet.
However this is a a good suggestion.
I might also offer Planet of the Vampires - I think it's pretty overlooked/forgotten outside of very aesthetic spheres, and it absolutely BLEW MY MIND when I saw it in 2000-ish, because it was made in 1965, but had aesthetics which still looker newer and cooler than 2000s-era SF in a lot of ways! It isn't a great movie but it is a fantastic one to look at.