> I have used only whole-disk XFS SSDs and HDDs for more than a decade.
I wouldn't recommend that. It makes the disk appear to be empty to many tools (and possibly some operating systems), which could lead to data loss. That's the reason GPT has the protective MBR: it makes the disk appear to be full to legacy tools which don't understand the GPT format.
You are right, and such disks will appear as empty to any tool or OS, but I will never insert any of my SSDs or HDDs that are used in this way in a computer that I do not control.
Windows frequently overwrites any bootable Linux drive, so it might have even less restraints with an apparently empty drive that does not have GPT structure.
Because of the risk of Windows messing with them, I also do not insert any of my bootable USB memories in a live Windows computer, even when they have GPT structure. For data interchange with Windows, I use only clean and non-bootable exFAT formatted USB memories.
While the space wasted by GPT and partitions and by the arbitrary alignment rules used by various formatting tools is not great, I do not see any reason why it should exist. The space wasted now with GPT and UEFI is several orders of magnitude greater than it was with traditional partition tables, so eliminating it has become more attractive.
Such SSDs and HDDs are not bootable, but for me this is a desirable feature, not a bug. I boot my computers either from Ethernet (e.g. most of my servers) or from a removable USB memory.
The SSDs and HDDs with a whole-disk file system are also wholly encrypted. As in a proper encryption implementation, there is complete separation between the encrypted data and the encryption key. The encrypted disks or their hosting computers do not contain any information about decryption, unlike in many systems of disk encryption. The encrypted decryption keys can be found only on external or remote boot media, which are not normally associated with the hosting computers.