I think it does not make much sense to protect the USB drive, as you won't be able to access it from another computer which is what USB drives are for. It makes sense to protect interval drives, but it is unlikely that someone would remove the drives and leave an expensive laptop to the owner.

I think of TPM-only more like a privacy lock than a deadbolt.

An encrypted external drive though works like a safe. Put things in there you want to keep safe but don’t need every day. Air gapped while not in use makes it even more safe.