Many historians work on manuscripts and/or large archives of documents that might not be digitized, let alone be accessible in the internet. The proportion of human knowledge that is available in the internet, especially if we further constrain to English-language and non-Darkweb or pirated, is greatly exaggerated. So there are infrastructure problems that LLMs by themselves don't solve.
On the other hand, people tend to be happy with a history that ignores 90+% of what happened, instead focusing on a "central" narrative, which traditionally focussed on maybe 5 Euro-Atlantic great powers, and nowadays somewhat pretends not to.
That being said, I don't like the subjectivist take on historical truth advanced by the article. Maybe it's hard to positively establish facts, but it doesn't mean one cannot negatively establish falsehoods and this matters more in practice, in the end. This feels salient when touching on opinions of Carr's as a Soviet-friendly historian.
My Dad, who is a professor of history, always used to say that being a historian is like being a detective, piecing together many different sources of incomplete or false information from unreliable sources, assessing motivations for actions, and so on.
You may indeed be able to establish some facts with high confidence. Many others will be suppositions or just possibilities. Establishing "facts" though is not really the point (despite how history is taught in school).
You try to weave all these different things into a bigger narrative or picture. It is most definitely an act of interpretation, which itself is embedded in our current conceptions (some of which are invisible to us and which future historians may then riff on).
Saying that you don't like the subjectivist take on history means you think there is an objective history out there to be had which we could all agree on, but that does not exist.
> I don't like the subjectivist take on historical truth [...]
The work of historians is to make inferences based on incomplete and contradictory sources.
Historians aren't simple fact-checkers. They make judgements in an attempt to understand the sweep of history.
You can see what kind of work they have to do every time you stare at some bullshit narrative put out by a company about how really it was good for the local economy for them to run their fracking operation, and the waste water really was filtered three times so it couldn't be causing the overabundance of three-legged frogs, and last year they funded two scientific studies that prove it. (I just made this up, hope you get the idea.)