I must be losing my love of books or something
That depends on what you've actually loved about books. Feel-good entertainment? Thought-provoking insight to the human condition? World view confirmation?
I read for entertainment and to unwind after my work
The analogy that EXPANSE is the Game of Thrones for science fiction is apt. It isn't there as feel-good adventure. So maybe your core premise for reading was off from the start, and its not the series for you.
If anything, I think THE EXPANSE reminds that exploration and colonization, doubly so in space, is HARD. And unforgiving. But the human spirit, and those who act with virtue, can prevail. That those with dark pasts (Amos) and regretted choices (Naomi) can find redemption on that hard path of doing what's right, not easy.
A Writer can't make a character's journey tough without making the reader's journey tough. THANOS isn't a scary villain if he loses to a bad but hopeful plan. And just because someone is "good" doesn't excuse or compensate for bad decision making.
Having the attention to detail and consequences that the EXPANSE does, I think its the BEST science fiction. Nobody is left off the hook by plot armor, or to make something upbeat.
The 4th book though, that isn't Science fiction per se (save for the Protomolecule secrets, backstory, and such). The 4th book is a Western, plain and simple. And a complex one on the level with THE SEARCHERS, HIGH NOON, or UNFORGIVEN. While they're emotional reads, ultimately virtue prevails. Not just being good, but being virtuous, and sticking to the struggle. The complex decisions, the grey areas, all that morality play is as fascinating to me as the application of simple Newtonian mechanics for plot purposes.
If the 1st 4 books were too challenging for your tastes, then I agree - do NOT proceed. Nothing gets easier from here on out. And the stakes, well ... lets just say while reading the 5th-7th books, I was more upset about things in the books than about outrages in the real world.
To get that sort of emotional engagement, that makes a book most precious to me. But I kinda crave catharsis when I read/listen/watch, so such stories aren't for everyone.
And please don't read judgement into all this - There are plenty of other works where I can't muster empathy enough to engage - for example, "Breaking Bad" - f**k that noise. Having seen some close to me have lives ruined by drugs, the premise of sympathy with almost any drug dealer isn't enough to get me in the door.