PoS coins have value because the marketplace dictates so based upon both utility and speculation.
This is mostly true and why I am a big fan of PoS coins. I think every Central Bank should have one.
Fiat really is an archaic form of PoS. Centralization also has advantages over decentralization. Decentralization is very costly and inefficient.
Decentralization is a form of chaos. The Bitcoin ecosystem is complex. Order emerges from complex chaos. It's called fractal.