Television

First of all, I agree with everything you said.

PS: spoiler warning for Thee Body Problem, so just skip that paragraph.

However, I think that deviating from the source, or adding stuff, etc, wouldn't be so destructive, if the writing was actually good.

Three Body Problem adapted by D&D, still felt a bit meh, because they made a bunch of changes that were just terrible writing. They didn't understand the source material, so they made the VR stuff alien tech. They made the stars blink, not the cosmic background radiation. The dimension folding fuck up leading to a giant eye over... Earth?... Why did they think that made any sense? It happened on Trisolaris, and it was such a goosebump inducing thing... Did D&D just think it might look cool, and... Since you cannot easily show it without showing the aliens... They kinda went "let's just do it on earth", even though it made no fucking sense whatsoever, because, they wouldn't have any reason to play a fucking prank on earth. Shits and giggles weren't their thing... Gah.

The Witcher suffered because the writing was actually quite bad at times.

Game of Thrones... I mean... I don't know why Dumb and Dumber get their hands on any work whatsoever. They have shown they know nothing of the world and systems they write for, nor characters or development. It's just embarrassing.

Halo, I haven't watched. And Fallout, I just know that Nolan and Joy are absolutely amazing writers. The only concern I had was to what extent people like Tod could fuck things up.

I think what I'm trying to add is that: Good writers can tell very engaging adaptations within the existing constraints of lore, world and rules, but it doesn't need to be existing canon. You can always tell new stories, as long as it sticks to the established rules and world building people expect. Bad writers fail at that, and often need to add contemporary trends where it doesn't belong. The fundamental issue might just be a skill issue.

Good writing is hard. It requires a lot of effort. You need to be congruent with the world and rules you've built so far. Not everyone will notice everything that deviates. Noticing bad writing is catching a lie given the presented imagined premise. Some suspension of belief is of course necessary, or risk being an annoying pedant. But, don't pretend someone is a level headed strategist, who then sends half their army out of a defensive fortification... to fight an enemy who is known to make dead soldiers fight for them. So which is it, do the people in charge know what castles are for, or did they suddenly become dumb as bread to suit some contrived narrative, or perhaps lack thereof?.. Gah..

J. J. Abrams didn't deviate all that much from lore. But my God what a grade A moron he is when it comes to plots points. Thousands of extremely talented master craftsmen, all coming together to tell a story... that only works if you don't think about it at all. And you might wonder which franchise in particular I'm referring to, as both apply.

The Expanse TV adaptation is a master class in doing everything right. TV is a different medium, and you cannot tell the story in the same exact way. But the changes they did, still told the same story, and most changes just suited visual medium better. They even had to off a character because of real life reasons, which was a little bit abrupt, but even so, they managed to adapt to that just fine.

Wheel of Time... weird additions and focus on romantic relationships that detracted from the magnitude and seriousness of the story itself. Maybe I was just a bit too young when I read the books, but I certainly didn't remember it like that, and it made the characters feel weird, and... immature. Also, somewhat intellectually insulting. Personal sacrifice, and love (? I'm looking for a better word...) for someone, doesn't require romantic interest.

I'm rambling.

TL;DR: Good writing good. Bad writing bad. Bad writing != not 100% aligned with source material. Contemporary tropes for no good reason = bad writing. JJ, please stick to directing. D&D... Maybe take up painting? Pretty please?