I will be less ambiguous. Just knowing your longitude and latitude and nothing else is not sufficient not for navigation. You need other stuff. Many gos devices provide other stuff other than position.
I don't think anyone is really disagreeing with you, you just seem to have picked a very strict definition of a GPS device which very few (given the number of mobile phones with mapping) fit within.
It's like saying: A map with just contour lines every 500m of elevation and nothing else is not sufficient for navigation (in the UK at least). You need other stuff on it. Many maps provide other stuff than just contour lines every 500m of elevation.
True, but a relatively pointless digression.
If I was dumped in the middle of the Atlantic ocean I'd rather have a device that could tell me my lat/lon than a map.
If I was dumped in the middle of Dartmoor or the Dales or the Peaks I'd rather have a good map than a device that could tell me my lat/lon.