Point 1 and 2 are contradictory. Point 3 I wasn't disagreeing with anything you said just adding my opinion to the conversation
I'll clarify. It is not absolute nonsense. It may be that they are more restricted, but the Expanse does not have the 50+ years of history of people declaring "This is Star Trek!" to argue about. It's a matter of interpretation, so they have more room to play, vs. Trek which must adhere strictly.
Indeed, The Expanse actually has deviated a bit from the novels, mostly at introducing characters on the show at a much earlier point than when they were introduced in the novels. Though they have also introduced characters original to the show who weren't in the novels, included subplots to the show which weren't in the novels and even killed off a character in the show who's still alive in the novels, though in that case that was done because the actor had to be fired from the show. Regardless, fans of The Expanse novels have reacted positively and embraced these changes. Whereas Star Trek fans are likely to react with murderous rage if anything in Star Trek gets changed and being preaching Gene's Vision or begging Gene have mercy.
Expanse didn't have time for a self appointed priesthood of gatekeepers to emerge. Discovery arrived with one already extant and well rested, ready to go. Of course, DISCO has developed its own gatekeeping staff, of late. Such things happen. Hell even MST3k went through its Mike vs Joel wars.
That's because The Expanse novels...aren't that good. I mean, they aren't bad at all, but they're sort of the SF equivalent of a Tom Clancy novel - plot-driven page turners. We're not talking Hugo material here folks. IMHO the biggest upgrade from the novels are the antagonists. They are all some variety of mustache-twirler or idiot in the books, while their portrayal in the show is far more complex.
Yeah, Klaes Ashford in the series is a much better character than the neer do well in the books, for instance. Sometimes a series or movie can better the source material. As far as comparisons between the two shows, I think it mostly begins and ends with how their ships look, and 32nd Discovery has traded in the dark look MOSTLY for the glowing blue Cherinkov Radiation aesthetic instead. I am glad of the new colorful uniforms for breaking visual monotony. They work very well in that regard. I suspect the directors were having that same problem in the last two years and were resorting to things like the turbolift funhouse, instead (will we ever actually see a turbolift, anymore?). But now that they have programmable matter, I hope we see more of it.
I guess someone should tell the Hugos. Leviathan Awakes was nominated for best novel in 2011. The Expanse has also been nominated for best book series twice, winning in 2020.