I'm well aware of logical partitions and how they work. As I said the 2TiB limit is on the disk size not the partition size.
Sorry I wasn't trying to insult your intelligence but my speculation was that a drive that was still using MBR and improperly formatted with one giant 5 TB NTFS partition would not be recognized by the router because of the 2 TiB limitations of MBR. I can't tell if you're agreeing or disagreeing.