Last month I saw a video discussing LOTR and why it shouldn't be taken as a true "historical" record of Middle-earth. Rather, it should be viewed more like an account "based on true events" viewed through the eyes of several of the participants. It also omits the accounts of the writers other than Bilbo and Frodo who worked on the Red Book of Westmarch.
This brings us to the Silmarillion. It reads a lot like the Old Testament, which is appropriate considering it encompasses several creation myths and even an analog of the Exodus. Of course, many things don't hold up scientifically. Tolkien was drawing more on myth than actual science, but let's take a look at a few examples.
Let's start with Arda. The Akallabeth states that the Numenoreans found that the world had been made round after the Drowning of Numenor. When I first read the story, I understood it as the world had always been round, and the Numenorean sailors discovered it to be the case. But it's commonly understood that the world was originally flat until Iluvatar changed it's shape. Later publications show that Tolkien was thinking of amending the tale to fit the round world theory.
Then there's the solar system. The Sun and Moon were not originally part of creation, and they can be considered artificial constructions (the same holds for the Silmaril borne by Earendil, which has been equated to Venus). The solar system is geocentric no matter the world's actual shape. But if Middle-earth represents a mythical age in the past, that won't work with our current model of the solar system.
Taking a different tack, let look at the captivity of both Maedros and Hurin. While the Silmarillion doesn't specify how long Maedhros hung on a precipice, later writings state that he was there for 20-30 years. Hurin definitely sat on his chair for a couple of decades. How did they survive that long? Did they eat, sleep, or defecate in all that time? Did Morgoth's power spare them the need? That's unlikely since Morgoth isn't known for being a nice guy.
All in all it can be argued that the Silmarillion is a mythical account rather an accurate record, although it was based on true events. This post went a lot longer than I intended. But feel free to share your ideas on this topic.