A blockchain is a distributed ledger with growing lists of records (blocks) that are securely linked together via cryptographic hashes.[1][2][3][4] Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data (generally represented as a Merkle tree, where data nodes are represented by leaves). Since each block contains information about the previous block, they effectively form a chain (compare linked list data structure), with each additional block linking to the ones before it. Consequently, blockchain transactions are irreversible in that, once they are recorded, the data in any given block cannot be altered retroactively without altering all subsequent blocks.

Yes they are. If you need an uneditable log, I guess? There are no uses on the blockchain for large file storage. Zero. It's a ledger, not a storage medium.

It's competing with Amazon S3, not Dropbox.

Distributed cloud storage sounds more like old torrents with partial seeders. But if you're using a chained ledger for that, sure. But like crypto, it's going to balloon out of control.