[janito]

I don't want to be pedantic, and I do agree that the scenario isn't centralization in a sense that it strongly threatens the network, but I thing there's a point here worth clarifying. Pools don't need their own physical miners to have power over the block generation process. AFAIK, the connected miners are "dumb clients", delegating their block generation capability to the pool in order to share rewards and therefore reduce income variability.

In short: the pool still defines the blocks that the connected miners will mine. They centralize all the collective power of all connected miners.