Agreed. JSON solves:

• the 'versioning' problem, where the data fields change after an update. That's a nightmare on packed binary; need to write so much code to handle it.
• makes debugging persistence issues easy for developers
• very fast libraries exist for reading and writing it
• actually compresses pretty damn well; you can pass the compress + write to a background thread once you've done the fast serialisation, anyway.

For saving games, JSON+gzip is such a good combination that I'd probably never consider anything else.