Hi Abhinav — yes, the emergence of large mining pools introducing a higher possibility of successful collusion was most likely not anticipated by Satoshi Nakamoto. While as a whole miners are not incentivized to blatantly or irreversibly harm the Bitcoin ecosystem (due to their interest in the value of the currency and their own, sizeable fixed price investment in mining equipment), you can see the potential here as when mining giant Bitmain initially announced they would not be supporting SegWit2x and threatened the community with a hard fork.
With regard to “true” decentralization, I recommend reading this article by Vitalik. He discusses how the term is very nuanced and should be considered from three facets (architectural, political, logical). Very interesting read.
