I'm talking about HARD AS FUCK SCI FI not hard sci fi. It's a distinct subgenre that i just made up.))

If we're getting scholastic about it then the whole 2001 series is something like Supple Sci Fi or Pliant Sci Fi or Springy Sci Fi or Firm Sci Fi playing more fast and loose with the technical side of things and leaning into soft sci fi aspects when it feels like it. There's probably a Brian Aldiss or Michael Moorcock essay about it already.

The Monolith and forces behind it are more or less plot devices up until they deus ex machina their way into the story once Bowman gets even with HAL. It's an age old tradition of sci fi movie third act clusterfuck. Technically, there is a whole bit of alien tech stuff going on in the books and it is not really ancient aliens and closer to reverse Star Trek with humanity getting Prime Directive'd. Funnily enough, parts of alien lore from 2001 and Rama were subtly merged with The Nomad in Star Trek The Motion Picture of all places.