That's true. Our Earth has lots of different biomes, environments and cultures making parts of our world radically different from one another. But in science fiction defense, uninhabited planets are usually just the one environment. Mars seems to be nothing but red canyons and deserts. But still the forest, tundra and ruins of Naverius was only so much territory. Maybe something along the lines of Iceland which has forest region and tundra region.
What I mean is, PSO2 covers only a small stretch of forest, tundra and ruins region that it's hard to call it a "whole planet" from just these areas.
Even PSO2:NG, while it's trying to be more like a single planet with open-world gameplay it's really just covering a small country so far. I doubt it's even bigger than Breath of the Wild Hyrule.
Or may be most of planets are indeed like that.
We say them small it's because we live such in big solid planet.
Jupiter, Saturn, Neptune, and Uranus, while they are bigger, are just gas giants, which means it does not have a solid surface.
No human or normal creature could not survive “on” Jupiter etc, because there's really no solid surface to be on.
Who knows what the majority sizes of the solid planets on the other galaxies.
