So the TLDR version: yes, you have to make changes when adapting a book but are those changes in service to the story the author wrote or to one you're making out of the shell of what the author did?
Personally I'd say, ultimately, all that matters is that you tell a compelling story which:
A) Basically has the same/similar themes to the original.
B) Doesn't like, actively burn down the original unless that's very much the intention.
And the WoT adaption absolutely was fine on both points, and indeed, I'd say it's completely impossible to reasonably argue the changes in WoT were not "in service to the story the author wrote" - indeed, they absolutely were in service to that story.
The problem really is that a lot of fans are incredibly precious about a lot of stuff that ultimately doesn't matter to the question you're asking. In many cases they have extremely unrealistic viewpoints about what can/should be changed about a story when adapting it, too. This isn't something unique to fantasy epics, either. Questionable supernatural romance novels have fans making the exact same arguments and having the the same "but you're changing too much" takes (c.f. True Blood and Vampire Diaries).
Telling the Wheel of Time on screen means you have to make some changes but it was a very different story, and I'd say it wasn't made any better for it. I am at best a casual fan of the Wheel of Time, but I know the hard core fans ripped it apart.
Yeah, many "hard core" fans did, but it's just silly to say that, whilst rejecting the same issue for LotR. "Hard core" Tolkien fans absolutely lost their minds over LotR at the time, and it took like a decade for them to calm down and reassess it as "not that bad, actually". If WoT continues I have no doubt the exact same thing will happen.
And "hard core" fans are THE WORST, frankly. Because they're the group with two huge problems:
1) They're obsessed with absolute minutiae, and are very often completely unable to see the forest for the trees.
The biggest "lore experts" are often people who don't even understand the themes of the books on even a very basic level. Like, with LotR, they can name every Elf in the entire thing off the top of their head, but they very often don't get
any of the messages Tolkien was trying to send. Because their obsession is solely with the superficial and the specific, not with the tone, not with the meaning, not with the message.
Again, this isn't just a LotR or WoT fandom thing - this is a consistent problem with every fandom where there's significant worldbuilding/lore - you can get tons and tons of "hard core" fans who absolutely obsessed with the series, but don't understand the series beyond the superficial. Everything from Star Trek to Steven Universe has these guys by the boatload. And there's no denying they're "hard core".
2) They're incredibly precious about specifics - even the ones who can "see the forest" often are.
Particularly serious fans will often have some single ultra-specific character or little bit of character history or even piece of equipment or whatever that they're ridiculously emotionally invested in. And like, I kind of get it. If someone remade Deep Space 9 and messed with Major Kira or deleted her from the story, I'd be mad as hell - but I would still judge the remake based on what it actually did - or at least not watch it and thus have no comment beyond "Messed with Major Kira, not watching".
That's not how most people behave though - instead they hate-watch - the know the thing they're extremely emotionally invested in has been changed/modified - and they still watch it, and then get really mad and absolutely castigate the show/movie and say it was the worst thing ever. The saddest is when they know something needed to be changed, and they get mad anyway.
There's also a subset of fans who get mad as hell about stuff that's entirely headcanon (particularly the sexuality of minor characters), or even outright misreadings (c.f. all the people angry that "they made Rue Black!" in the Hunger Games movies, where in the books, Rue (the competitor, not PRUE, Katniss' sister), is clearly described as dark-skinned and curly-haired. They're even worse, but let's discount them for now.
When it comes to WoT, it did help that when the first books were first being published in the '90s, it was the one big series that was doing things diffferent and subverting tropes in the fantasy genre. That became far more common later on, especially after GRRM completely upended everything.
What is it about WoT that you would say subverted fantasy tropes?
I would say that, based on the first two books and knowing the entire story of the rest (but not having read the actual books), in leans extremely hard into very traditional fantasy tropes, though nicking a bit from Dune and Western takes on Eastern religions.
I'd really say I thought his success was down to the opposite - he was one of the authors in the 1990s hewing closest to standard fantasy tropes.
Especially after 1995/1996 when there's an absolute NUCLEAR EXPLOSION of trope-subversion. You mentioned
A Game of Thrones in 1996, but we also have
The Golden Compass (1995),
Wicked (1995),
Tigana (1990 and ultra-subversive of tropes),
Neverwhere (1996),
Assassin's Apprentice (1995),
The Gardens of the Moon (1999),
Ship of Magic (1998),
Imajica (1991),
King Rat (1998) - I could go on, I know I'm missing tons.
Steven King's Dark Tower series had been going for some time by then, and whilst it's not all subversion, I'd say it was far more subversive of tropes and did things far more differently that WoT. Plus Terry Pratchett, but because it's humourous maybe it doesn't fit the same niche?
For my money, Robert Jordan fits solidly into one of the "big four" trad-fantasy authors of the 1990s:
Terry Brooks (Shannara), David Eddings (Belgariad), Robert Jordan (Wheel of Time), Raymond E. Feist (Riftwar)
(Could include Tad Williams and Stephen R. Donaldson maybe too? A lot of important female fantasy authors in the 1990s but none of them were writing fantasy quite as trad as the above four.)
They all did things a bit differently to Tolkien, but like, it's still clearly trad-fantasy in all cases imho, and tropes remain fundamentally un-subverted even if specifics are changed.