I've been partitioning all my PCs' drives for some years. That they don't come this way is almost criminal. But I'm wondering if there's the same issue with a Fusion Drive (first I've heard of it actually), as they are physically different.....maybe there's an option in the firmware to wipe only one drive at a time?
I don't see a need to write to a separate drive by itself (though the data partition being synced to another drive makes sense), though if the practice is moving to SSDs for OS, and standard for data, then there's no issue.