Seems like any Database could be used for this. If there is a central authority its almost certain no blockchain tech is needed at all. A central authority does

Seems like any Database could be used for this. If there is a central authority its almost certain no blockchain tech is needed at all. A central authority does not disabled swarm intelligence or something. It does not have to use its power against all others. Centrality ruled systems work very very fine as long as the central authority has the same goal as the other parties. If there is a central operator for anti spam call database and they do their job correctly there is no reason to not trust them and replace them with complex distributed agreement mechanisms. especially not if they in the end are in control of "the blockchain" anyway.