Yes earth was:
Before humans came, and still is. Problem is real planets are typically of only 3 main types:
1. with atmosphere which gives different biomes (see earth)
2. dead rocks
3. gas (no solid surface, like jupiter, so no buildings, settlements, agriculture possible)
There is no "forest-planet" where poles and equators and everything is "forest". This is a fantasy-game not a astro-simulation so it might not matter, but its almost always disregarded in these 4X games.
Maybe a game could still use the more realistic approach somehow:
1. Livable worlds. For population and food production and mines. "Best" planets for the player. Portion of different biomes can vary.
2. Rock world: still can be mined for resources (can have moon-base styled colonies, maybe heavily mechaniced?). No farms.
3. Gas planets: not landable, but maybe useful for something else?