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The point is that mining is becoming more decentralized, and this much reduces the likelihood of "cartels".
I'm not sure I would take anything as a given just because someone made a colorful pie chart. Specifically, it is known that an entity with a high percentage of hashing power freaks people out. Were I running an outfit who had the potential to form such a pattern, I would split things up long before a threatening pattern emerged. Behind the scenes at a social level reality might be quite different.
Secondly, I don't find it very easy to get much of a sense of how many chips are in a noisy box someone's back room vs. how many are submerged in an oil bath in some datacenter. Either type could change behavior slightly to influence the pie charts, but there would be a variety of differences in why they would do so and what impacts it would have.
Thirdly, and somewhat related to the above, if a pool for some mysterious reason started to give miners and extra good deal, I would expect that a fair fraction of the home-owner types would not really stare a gift horse in the mouth and jump on over. Even if they knew in the back of their minds it was a bad idea for the ecosystem it would be sorely tempting to leave it to the other guy to try take the bullet. This especially if it's the difference between a profit and a loss, and the gear one is running is approaching obsolescence anyway.
I sense sort of a desperate hope on the part of the naturally hopeful in these discussions of mining centralization. Certainly I'd want fewer unknowns and more knows before I was very comfortable with huge fraction of my net worth riding on Bitcoin.