Blockchain is not necessarily "distributed", in the sense that multiple competing parties have a copy of it. As an example, hyperledger fabric is commonly used

Blockchain is not necessarily "distributed", in the sense that multiple competing parties have a copy of it. As an example, hyperledger fabric is commonly used as a "private" blockchain. Also, it is trivial to implement the same verification mechanisms in traditional databases, without the performance penalties of "blockchain", and transforming them in immutable, append-only storage systems that can't be tampered transparently. A good example of this is google trillian, the backend used by Certificate Transparency implementations.