Agreed. I definitely wish there were more dark levels in games, so long as there's a way to see that you aren't dropping off of a cliff but the rest is simply terrifying. It really opens up those levels to have amazing sound design.
I think it's hard to do those levels well, though. Too many horror games try and miserably fail to deliver the suspense that comes with darkness (I can kinda excuse indie games because of the nature of their creation, but professional games do it too and that's just a sin). I think it's also just too easy to overdo, and not enough people focus on sound design to make it truly creepy and instead focus on the jump scare options that darkness offers, even if it's unreasonable to do.
I think that can work well, depending on the gameplay you want. Fast-paced sprinting in a really pretty environment takes away from the environment being pretty. A sci-fi game based on exploration of the unknown planet can be baller as hell. Subnautica, as case in point. But if you're going for an FPS, a beautiful, unknown planet would be a waste for that.
Also, this setting you described is shockingly like something I wrote couple years ago. It was post-human mass extinction and it was gonna have some exposition about humans being manufactured as a species and the planets belonged to their progenitors, who experimented in genetic exploitation and creation of monsters that eventually killed them all. Spurned creation kills the creator and all that. Kinda like what Prometheus did, but better and without a disappointingly predictable ending, and I wrote it before that movie came out.
Had a ton of scripts and shit, as well as a multi-planet system mapped out that had planets with different environments for different laboratories and creatures. Was a full exploration-based RPG with a touch of action and small amounts of creepy shit. The people I was working on it with were asshats. Even had some of the more basic programming and art done for it.