It's not so much about reward for node who produce blocks, but about proof that enough nodes on the network validated it aka solution to byzantine general problem. Otherwise , it's back to trusted nodes, centralized authority, etc, and the cost of operarion are then minimal.
I am not arguing that rewards to maintain consensus are unnecessary, just that inflation-based rewards are likely unnecessary.
I understand the reasoning for the necessity of block rewards, and do think they are necessary for PoW cryptocurrencies. But for PoS variants? I don't think that inflationary rewards are necessary.
Maybe PoS variants are not ideal as far as decentralization zealots are concerned. However, for 99% of the worlds population- they do not care about that kind of thing and PoS cryptocurrencies are sufficiently decentralized as is.