Isn't this also its biggest drawback? If every node has equal say we need to have additional complicated logic to ensure consensus, while in a centralized system we do not need to this, since a centralized system is a source of truth and the only writer?

The same logic applies to less decentralized systems like NEO that have a predefined set of voting nodes. Less nodes, means that we need less effort to achieve consensus, hence higher performance.

So the question is: in what use cases truly decentralized systems cannot be replaced with not so decentralized systems?