PoW cannot be totally discarded or remain redundant like that. It is even too early to conclude that one has advantages over another because of Ethereum shifting to PoS. Blockchain technology is still young and let's wait and see how all these things will play around in the coming years.
Isn't it enough to saying that if POS has more advantages compared with POW in term of the energy and resources consumption? Ethereum will not even migrate to the POS if that was not offering a lot of advantages too. Let's assume of both are having advantages and disadvantages.
POS just reward the richest and this can be determined which is like a centralized way of wealth distribution, but POW distribute wealth fairly to a specialized miners who have a consistence dedication of their equipment to the project and this us random and no can determine this reward distribution.
Isn't it also POW only rewarded the big miners? Remember the small one will always lose the domination and rather adding more and more GPU and it's better to make the token at least becomes more useful to the buyers.
No doubt POW is losing popularity, and most of the projects are shifting to POS like Ethereum and the new coming project also adopting POS because POS is easy to mine and no need more power, and everyone can easily take POS.
POS is not a mineable token and remember this.