Yes, You May Need a Blockchain

Can these actors interoperate? Can their users pull their data out and bring it into other applications? And given that the users are themselves economic actors, if this data represents something of monetary value, can the users be confident that their data wasn't modified during all this exporting and importing?

No - different applications typically don't have interoperable software, or allow their users to easily export/import their data in a standard form, or give users certainty that their data wasn't intentionally tampered with or inadvertently corrupted during all the exporting and importing.

For most major internet services, there is simply no financial incentive to enable users to export their data, let alone to enable competitors to quickly import said data.

While some call this the data portability problem, let's call it the data export/import problem to focus attention on the specific mechanisms for export and import.

Some businesses do let you get some of your data out, or give you the ability to write data to your account.

While CSV represents tabular data, MBOX represents a type of log-structured data.

Public blockchains convert many types of data import/export problems into a general class of shared state problems.

Because the data associated with a public blockchain represents something of monetary value, it finally delivers the financial incentive for interoperability.

We've now got a reliable way to incentivize the use of shared state, to simultaneously allow millions of individuals and companies access to read from the same data store while enforcing a common standard and maintaining high confidence in the integrity of the data.

There's ongoing development on public blockchain versions of things like OpenStreetMaps, Wikipedia, and Twitter as well as systems like Filecoin/IPFS. These wouldn't just represent records of financial transactions where immutability was a requirement, but could represent other types of data that would be routinely updated.