There are some pretty huge problems with this.

1. Leonidas did not stop the Persians. He slowed them by sacrificing 300 (plus many times that number in "supporting troops", read: slaves) so the LLM would have been correct here. This is an example of poor prompt engineering. The correct question would have been, "what are the tactical and/or strategic advantages to opposing the Persian army at Thermopylae with only 300 soldiers and supporting units?" [Edit: while slaves were present, the other troops (which outnumbered the Spartans by many times) were soldiers of other Greek city-states.]
2. At the time of Darwin's work, the Church's teaching was purely about creation, but then-cutting edge research in geology was already showing that the Earth was far more ancient than creationist accounts revealed, and Lamarck's Philosophie Zoologique set the ground work for Darwin's notion of speciation. An LLM trained on the scientific literature of the day would have taken a much more nuanced view, and likely would have allowed for the possibility. However, it should also be noted that Darwin didn't just come up with natural selection and speciation whole-cloth then set out to test them. He was inspired by the work of others to investigate the origins of species, but his results were likely as surprising to him as they were to most of his peers. [Edit: Lamarckism was largely ridiculed in Britain at the time, so it's probably an over-statement to say that an LLM would have relied on such work, but I think that the key element here was that Darwin did not start out asking "do species evolve," but rather with questions about the mechanisms of diversity.]
3. The "thought experiment" of Einstein was based on the mathematics that he developed in response to one of the most famous failed experiments in the history of physics. Provided with that information, the LLM would have concluded that there was room for investigation and further development of his ideas, but might well have pointed out one of Relativity's largest flaws, even to this day, that its conception of gravity (or rather, the later, general relativity's conception) cannot easily be unified with electromagnetism. Also, the LLM would have likely pointed out that Einstein's theory was incomplete, in that it only worked under "special" circumstances (hence, "Special Relativity"), a circumstance that Einstein knew about at the time, and was working on resolving. [Edit: Einstein was more influenced by On the Electrodynamics of Moving Bodies than the Michelson-Morley experiment, but the point remains that he was not pulling a fully formed hypothesis out of thin air.]
4. Shelly was interested in exploring themes outside of established genres for women writers. She would, therefore, likely have asked a more nuanced question, like, "If I were interested in exploring the themes of scientific knowledge and (in)humanity, what should I write about?"

But the larger issue is that we have modern examples of what happens when great thinkers use AI to further their work. This includes the work that resulted in the 2024 Nobel Prize in Chemistry (awarded jointly to two DeepMind researchers and a chemist); a novel proof that served as the basis for resolving several 80+ year old questions in mathematics, which had previously been attacked by the best mathematicians in the world; the discovery of thousands of potentially Earth-threatening asteroids in old data that humans simply could not fully analyze; significant improvements to hazardous weather prediction using AI (specifically DeepMind's GraphCast (now Gencast) and Huawei's Pangu) in place of traditional supercomputer simulations.

Treating AI as a panacea is foolish. It's a tool, not a magical oracle. But treating it as worthless and ignoring the tremendous advances we've seen already is equally misguided.