If one looks at the sky through the eyes of a 7th century camel herder or caravan navigator, it becomes much easier.
In my opinion, the seven heavens or seven domes actually represent the pagan concept of the gods on seven objects in space known in the 7th century (Sun, Moon, Jupiter, Mars, Mercury, Saturn, Venus or ?naked eye planets? according to the Ptolemaic theory) until the observations and research of Copernicus put an end to that. Corresponding to the seven heaves were seven Hells, as so vividly described by Dante. There are other descriptions of different models of Earth or many earths and each with domes over them. Whatever the ancient description may be, none of them in any way represent a scientific fact or reality.
I agree with you that its about what the people can see or what can be known through human observation. But its also talking about what is in our domain (ie solar system) There are seven planets besides Earth. Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune. These represent seven major orbits.
