So in other words, an arctic planet is what, a planet whose entire surface is a uniform temperature that emulates earth's arctic circle?
Well, Mars is a planet whose entire surface emulates New Mexico or Nevada or something, and Venus is a planet whose entire surface emulates the inside of a oven filled with poison. So, honestly, I don't think it's that implausible.
If an arctic planet is just a planet whose average temperature is equivalent to earth's arctic circle, then that means that parts of the planet must be perfectly habitable for species who are accustomed to warmer temperatures, just by virtue of an average on a temperature gradient requiring both warmer and colder temperatures.
An article planet is a planet whose warmest equatorial regions are equivalent to the article circle, and whose coldest regions are far colder. A species who lived there would think of their equatorial regions (assuming the planet's axial tilt is the same as ours) the same way we think of the poles: a remote and inhospitable part of the planet that they can only live in with special equipment. Somewhere like earth would be out of the question for them, without special technologies.
Also? Two words: ice age.
Double also: a biome is about more than temperature - tiaga and steppe are both biomes, and they're both fucking cold. An 'artic world' could be as diverse as earth in terms of environment, just a hell of a lot colder.
The reality is that no planet is uniform in temperature, and especially any planet which falls within Earth's temperature gradient is going to support diverse biomes thanks to water's reaction to temperature. A slightly colder or slightly hotter planet just may have more of one than the others.
If you put earth where mars was, it'd be an ice ball except for a few regions during summer, which would be what we'd call slightly warm.
Which is why biome planets are a silly star-warsian trope, and I was disappointed in them the moment I heard about them. But it's not a deal-breaker. Gaian planets just fail to make sense within the abstraction they have created, because it references mechanics that other planets utterly fail to represent. Latitude is a factor which makes Gaian planets great for everyone, but other planets don't have latitudes which result in temperature gradients? What? Why not? Why are we supposed to accept one explanation when the entire rest of the game handwaves that explanation away?.
The tile system is abstract as fuck. I don't think it's even supposed to represent distinct regions, because otherwise why would people be evenly distributed across the surface? There appear to be no cities.