How does Pokémon Legends: Z-A fit into the Pokémon timeline?

Pokémon Legends: Z-A is a bit of an odd game in the Pokémon timeline, if you care about such a thing. It serves as both a sequel to Pokémon Legends: Arceus, a historical game set in feudal Hisui, and Pokémon X and Y, two RPGs set in a modern region inspired by France. Before its launch, I wondered how exactly The Pokémon Company was going to thread that needle, distilling two very different settings and histories into a coherent sequel.