The upside is that we can differentiate between the quality of various competing hypotheses in a reasoned way. That's how we can say that the traditional academic narratives are epistemologically better than e.g. Tolkien's Silmarillion.
[1] https://doi.org/10.1130/0091-7613(2001)029<0987:HSESAT>2.0.C...
In recent memory just about everyone was dead certain that monumental architecture happened only where there was agriculture. And, that once a people took up agriculture, they kept at it. And, that humans got to the Americas no more than 15,000 years ago.
Science only welcomes new ideas when they offer a possible solution to a problem with the existing paradigms. For this type of theory, if you had data showing the earliest known societies were unusually advanced, or if you had artifacts that suggest more wide spread early societies, these would be facts wanting an explanation.
You can't just say something like "maybe all language was singing until 20,000 years ago" and claim it's scientific until proven false.
We know there are human built megalithic structures that are dated at the end of the Pleistocene. We know that the Pleistocene ended abruptly with all North American megafauna perishing and immense amounts of meltwater entering the oceans. We don't know if there were a bunch of distributed civilizations with similar technology levels or if there was a global civilization that shared knowledge before or after cataclysm. We also don't know what caused the end of the Pleistocene. This is the realm of hypothesis on all sides.