I'm listening through the audio books while I was on my third watchthrough. Finished the watchthrough but now I'm on nemesis games, which I think runs pretty much to where the show ended. Definitely worth going through both! The stories diverge in some major ways, but also run pretty parallel.
The Epstein drive is key to making the story actually work though, without it all the travel times would be elongated and the whole thing would fall apart. Honestly I think they did an amazing job of keeping the fictional science to a minimum, including the Epstein drive (although protomolecule stuff is basically magic).
It's a lot less fiction than many other fictional spaceships. It's not an FTL drive or anything, it's just an ordinary rocket engine with an extremely high Thrust-Weight ratio
I have a running theory that the best grounded sci fi get one big free technology that doesn’t need to be based in anything realistic whose implications create the rest of the setting.
In Mass Effect, it’s the mass effect created by eezo that allows for gravity manipulation. It’s how cars can fly, ships can travel between planets, and biotics get their superpowers. It allows the universe to ask “how would the world be impacted by gravity manipulation?”
In The Expanse, at least leading up to the events of the first book, it’s the Epstein Drive. How would continuous thrust allowing for interplanetary travel over days/weeks instead of months/years affect society’s growth? It allows for a more rich and interesting world by only asking for one strong suspension of disbelief.
What makes you say the Epstein drive is pure fiction? If we can figure out fusion, it's probably not that far off. Constant acceleration is a powerful force.