> When it sees a certain string in any write to the disk
dm-crypt or zfs encryption or any other commonly used encryption will encrypt the data before it's written to disk, so the disk controller will not be able to do anything with writes or reads since it will not have the encryption key.
If I'm doing software encryption like dm-crypt or zfs encryption then I don't need to bother with hardware encryption too. It's easier to trust software encryption. We have many interoperable and even open source implementations of the same encryption methods, the output is readable in open formats, so they can be validated against each other if needed.
The people buying much of these "hardware encryption" products do so because they believe it removes the need for software encryption to/from the device.
Everything you wrote is not an exclusive Lenovo risk and vulnerability but applies to every piece of compute sold in the worlds.