> Some filesystems have a richer interface to the underlying storage device, allowing them to invoke commands such as ATA TRIM or SCSI UNMAP

No, that's not a guarantee of data erasure. Not just because it's just a request that the device can disregard, but also because filesystems play tricks (like storing small bits of data inline, or logging data in various places, etc.) and they don't clear all those blocks just because you wanted to clear a couple bytes.