Well, that (and the shots showing several Jupiter moons simultaneously) was a creative decision - one I strongly disagree with - but otherwise The Expanse is pretty good, and they get lots of minor details right (like engines heating up some metal beams on the exhaust path, or that scene where a PDC round penetrated the Roci and its trail didn't move until they started manoeuvring, etc.).
That and the ships having to flip to slow down burn makes the expanse one of the more realistic portrayals of space flight (minus the epstein drive which is basically magic) in modern tv.
Also, they show decompression way more realistically. Its not like a bomb goes off when a hole opens up in the side of the ship, which is nice.
assuming an epstein drive is possible yeah it opens up more or less direct brachistochrone trajectories between here and mars. Just wait until the planets align and burn.
It's a lot better than people think fusion rockets would be in real life. But the writers actually acknowledged that, in the episode that goes into the drive's history. They had fusion rockets before Epstein, they just weren't near as good before the breakthrough.
And most of the story wouldn't even change if it took longer to go places. The only difference would be that they couldn't show normal gravity inside a spaceship and attribute it to acceleration. It's a slight distortion that saves them money on special effects.
They especially don't show long travel times, but in the books travel is usually counted in weeks or months. Also, in the books they usually travel at ~0.3g for the sake of Martians and the Belters, who are mostly not comfortable with Earth's 1G.
(This is not merely a detail, it's one of the core plot points of The Expanse, as tolerance to gravity is what makes Martians and Belters almost a different species from Earthers; the former can not live on Earth, and so they don't care much about it.)
I don't actually recall what the in universe explanation of it was outside of it running off water as its fuel. Either way its specific impulse is crazy.
There was a scene in the first episode that drove me crazy. They were on the ship hull after a huge explosion had occurred. Tony debris kept flying by in the background at what looked like 30/mph. That broke immersion for me so bad.
