OP here. I was expecting something called a "Microsoft Signature Device" to be similar to a Nexus device, wherein MS was working with the OEM to make a sort of reference device for the form factor. Nexus devices usually don't have the latest-and-greatest, and they still work pretty damn well.

What I got out of this instead is that MS guarantees a "Signature Device" to just be free of any bloatware. I was also deceived by the devices in-store working perfectly well, but having been already fixed by store employees before customers could get to them.

Guess I know better for the next time, eh?