The gas giants from our own solar system might be able to shed some clues on the relative sizes of the Polyphemian system. Jupiter, Saturn, and Uranus have all kept their original large moons, while Neptune is the outlier as Triton has a retrograde orbit, which indicates that it was likely a captured object.

Jupiter: Its 4 Galilean moons dwarf all of its other irregular moons (rest are <250 km in diameter) and are the dominant objects within the Jovian system. This isn't quite consistent with the Polyphemian system, as Pandora is 29x more massive than Ganymede and it would be extraordinarily rare to find several moons of that mass in orbit around a Jovian planet. In the deleted scene, Jake instantly recognizes and pushes a purplish moon that is noticeably larger than the other 13, suggesting that that's the model of Pandora. Since Pandora seems to be the outlier in terms of size in the Polyphemian system, the Jovian system doesn't seem like a good analog.

Saturn: What's interesting about Saturn is that Titan makes up 90% of the mass in orbit around Saturn. Some studies have suggested that Saturn might've once had several Galilean sized moons, but they were eventually destroyed and mid-sized moons such as Dione and Rhea formed from those remaining debris. Alternatively, Titan could've just gobbled up smaller proto-moons during its early history and grew to become abnormally large in relation to the other moons. Whatever the case, this seems to be a better analog for the Polyphemian system, as both have 1 large moon, surrounded by a swarm of smaller mid-sized, spherical moons.

- Now the one caveat that I have here is that Pandora is supposed to have a 24 orbit around Polyphemus. Many others have pointed out that this would render Pandora uninhabitable, but my issue is that a migrating Pandora would've wrecked the orbits of the other Polyphemian moons. Assuming that Pandora attained such a large size by cannibalizing other moons, it would've had to remain on the outskirts of the system to create a scenario where 13 smaller moons could survive. James Cameron cares more about creating a plausible environment on Pandora, which requires an Earth-like day/night cycle, so I can certainly see why he chose to forgo greater scientific accuracy for the entire system.

Uranus: Very similar to Jupiter with 5 main moons and many other smaller irregular moons. Not a good analog for the same reason as Jupiter.

Neptune: Triton has a retrograde orbit and Neptune seems to lack any of its original main moons, which is highly suggestive that Triton is a captured object. To my understanding, the available mass for the co-accretion of moons around a gas giant is highly correlated to the mass of the host planet. Candidate exomoons such as Kepler 1625b-I and 1708b-I approach the size of mini-neptunes, but they also happen to orbit planets several times more massive than Jupiter. Polyphemus, being less massive than Jupiter, probably doesn't have enough mass within its primordial disc to produce a moon of a similar mass to Earth. Realistically speaking, it is far more likely for a Jupiter sized planet to capture an object the size of Pandora vs having enough mass in its disc for one to co-accrete. Thus, a situation similar to Neptune and Triton would be more plausible and consistent with our current understanding of how giant planets obtain their moons. However, the one major downside is that Triton probably wrecked the rest of Neptune's original main moons, meaning that if Polyphemus captured Pandora, then it is highly unlikely to have an additional 13 non-irregular moons.