I heard that most of the miners are located in China. Thus we can say that most hash power is controlled by some regions. Can we still call Bitcoin decentralized if its backbone infrastructure is so centralized?
It is not a problem anymore, Bitcoin is just too big than worrying about some regions mining more than the other, because right now Bitcoin miners are everywhere, almost all countries in the world have atleast someone mining Bitcoin in them.
The idea is getting out of one man's control and this have become a success for many past years now, the hash rate war is already over, in my own world though I don't know about others.
Now to answer your doubt, Bitcoin mining is obviously more decentralized as one man or one entity can't control the hash rate anymore, it has grown beyond the control of one person.