What ultimately matters is decentralization. As long as ETH remains decentralized, there should be nothing to worry about. Just my thoughts 
But how is Ethereum able to remain decentralized when it is fully moved to the Pos network? I like the idea that ethereum might move to POS , as this could be a first step towards expanding further and reducing gas fees when other updates are rolled out in the near future. But what I'm still a bit worried about is that it will become more centralized than the decentralized network it used to be. What are the ethereum developers planning in this regard?
They are very clear though that it won't solved or reduced the gas fees and this is the common misconception that they want to clear. For sure it will be more centralized, the validators will have more control of the network.
And so with that, I believed that they will be more centralized as you have said. But it will only time can tell if they make a good move or not, giving so much power to the validators and those who have their 32 ETH stake.