1. Each tier is its own game, 2. The games are not independent
As a simple, two-game, example. Imagine a strategy game such as Shogun (turn-based strategy). When the players kn that game start conflicts that opens up a match for FPS-type players to join. The outcome of the battle will depend on the FPS-player performance while the match-up is skewed depending on the relative forces deployed by the generals.
Maybe cities are maintained by more Minecraft-esque players, while the eye in the sky can submit tasks down below for resources, certain buildings, etcetera.