I do agree that proof of stake is a genuine improvement on the cryptocurrency concept, but I think it's fair to hold off on calling the problem solved: Bitcoin and other popular networks are not really any closer to adopting it, and there still remains some skepticism about potential failure modes. Proof of work is a bruteforce solution, but it's quite proven and the failure modes are pretty straightforward. Proof of stake seems to work but it's a bit of an ouroboros.