A crucial difference is that Gibson hasn't the faintest idea about the actual technology - he wrote the early stuff on a typewriter - whereas Stephenson has a least a rudimentary understanding. For lots of readers this doesn't make any difference, but if you actually have some idea what's going on Gibson's approach interferes with the immersion more than Stephenson's.
This has some impact on predictive power too. One reason people tried to build the Young Lady's Illustrated Primer is that - more or less, you actually could imagine building that. My friend's daughter talks to the AI, and is learning to read stuff on a glowing screen that knows her name. She doesn't have an abusive step-father, and so fortunately her glowing screen won't need to teach her martial arts for people who are smaller and less powerful than their opponent, and about the importance of running away when there's no way to win. And hopefully her mother will remain a loving physical presence in her life. But the general thrust of the idea in the Primer makes sense, even if we aren't close to "really" building the Primer, ideas from Gibson don't make so much sense.
To me I think it's the opposite -- the fact that Neuromancer's technology isn't just a version of what we have makes is what makes it timeless. Kind of how Star Wars tech from 1977 seems less dated than in most SF movies because it wasn't based on real tech. Snow Crash is so obviously just 1992 technology with a coat of paint -- Stephenson obviously played MUDs and that's all his virtual world is -- a MUD. And so it hasn't aged well as MUDs weren't the future.
I guess in some sense I agree that "MUDs weren't the future" but they are in fact all that anybody keeps building. Facebook's "Metaverse" is just a shitty MUD, likewise for various "Blockchain" projects that produce some sort of virtual land where you... sort of stand around. The art project I visited at the weekend with a friend had a VR environment which was too limited to really be much of a MUD, but it certainly wasn't anything more than a MUD.
Science Fiction isn't necessarily about "a version of what we have" but it is about the What If? question and fantasy stories don't address that. Unexpected consequences are the story seed in good SF. Asimov in the 1950s notes that a good SF story predicts not the automobile but the traffic jam. That's where I think Stephenson is good and Gibson has nothing to tell me.
Star Wars says Space Wizards fighting laser sword battles may not vanquish Evil and I'm like OK, cool, but so what? Diamond Age (in some sense a sequel to Snow Crash) has a bunch of interesting things to say about society, about what parenthood means, about Cultural Imperialism, and about what we/how we teach children.
I'd argue that Gibson had the most important social prediction in cyberpunk -- one that we kind of ignore today because it became true. In Gibson's future, the real conflicts are not between national governments but between rival tech companies. Obviously Gibson made the mistake common in the 1980s that the tech companies would be Japanese rather than from US or China, but the key prediction was insightful. Later cyberpunk authors like Stephenson also often have megacorps, but they obviously took them from Gibson.
The Vicky companies in Diamond Age are basically John Company, the British East India Company, I think it even more or less says as such, calling it John Zaibatsu. The Victorians appear to live in a plutocracy, but it's very particularly a Victorian plutocracy, we don't see any poor Vickies, the thetes living down in the LT are not Victorians and nor are the artisans on the hillside. The nature of the Mandarins is unclear, whether Doctor X is unusual in operating an actual business close to the LT, or whether actually the Middle Kingdom, too, is controlled by businesses and the Mandarins are the owners.
And as to the idea that it became true, well, here in the real world it is Russia that invaded Ukraine and not an invasion by Gazprom or whoever. The sovereign entities are still fundamentally concrete in a way that a corporation is not.
The Fists in Diamond Age may in some sense be tools of the Mandarins, but certainly the Mouse Army don't work for anybody except Princess Nell, their loyalty to her has been blended into all their learning from infancy, almost without anybody consciously intending this (Hackworth is ultimately responsible, but if/why Hackworth chooses Nell rather than his own daughter is unclear, we don't see enough of the other copies of the Primer to discern whether the other two girls could have led the Mouse Army, the novel is about Nell).
The land war between Russia and Ukraine that's happening right now, and the decade+ of land war the US waged in the Middle East before that, make me think any bickering between Google and Apple still look worlds away from corporate-conflict dystopia (of course, this is a critique that also applies to Snow Crash and The Diamond Age, which were corp-heavy).
There's a whole chain of this thinking in SF. Asimov was the first to use the analogy in the 1950s though he never chooses the exact phrase "traffic jam":
Pohl in the late 1960s acknowledges that he isn't the first to have this idea, but does actually use "traffic jam": “Somebody once said that a good science-fiction story should be able to predict not the automobile but the traffic jam”
I rather like Heinlein who a little earlier (1966) suggests SF would have predicted something more interesting, instead of car -> traffic jam, Heinlein says good SF would have predicted car -> teenage fumblings in borrowed car.
This has some impact on predictive power too. One reason people tried to build the Young Lady's Illustrated Primer is that - more or less, you actually could imagine building that. My friend's daughter talks to the AI, and is learning to read stuff on a glowing screen that knows her name. She doesn't have an abusive step-father, and so fortunately her glowing screen won't need to teach her martial arts for people who are smaller and less powerful than their opponent, and about the importance of running away when there's no way to win. And hopefully her mother will remain a loving physical presence in her life. But the general thrust of the idea in the Primer makes sense, even if we aren't close to "really" building the Primer, ideas from Gibson don't make so much sense.