Your starting point is wrong, so, all the deductions is wrong as well. If you want to see the hash rate distribution, well, that's public information, so feel free to take a look at:
I think that you do not understand what centralization of mining means. It's about the right to issue Bitcoin. This is a matter of economic and social level. Bitcoin was not invented in order for several billionaires to become multi-billionaires. It was invented in order to free ALL MANKIND from the Central Banking System.
Now Bitcoin is like an ordinary Bank: big commissions, long transfers, Big Brother control ... This violates the principles that Satoshi announced in his Whitepaper.
And it needs to be fixed!
Until you see a pool with more than 51% of the network you can say mining is centralized.
It has already happened once and can happen again.