Earlier quoted context omitted.
"Edge" refers to the edge of the device. There is no other edge metaphorical or otherwise, imho. More than definition, how metaphors are used is important. Is "edge" a metaphor when the actual edge is right there, 9mm from the screen perimeter? There is no metaphor only 'edge-to-edge' window dressing. In the same way "lightning" is not a metaphor in a discussion about thunderstorms.
As others have advised, you should look up how metaphors are used, See my other comment in this thread, there is at least six years of prior usage by multiple big tech companies describing their product's screens as "edge-to-edge" without literally meaning edge-of-device to edge-of-device, with links. And see my other other comment where I wonder why "edge-to-edge" has your goat, when Apple describing the iPad Pro as…
Irrelevant. This discussion was about the one and only use in town right now of "edge-to-edge" in a major campaign to sell new tablets.
"All screen" is more ambiguous. For starters "all screen" is not a pre-existing term. It could be used to mean there's no other elements or buttons on the front, except the screen. "All screen".
"Edge-to-edge" on the other hand, has explicit meaning built in. The primary component of which is measurement. "Edge-to-edge" refers to not one, but two hard edges, and describes that which spans in full from one edge to the other. There's no vague interpretation possible unless you force a square peg through round hole of English. It's either an edge-to-edge screen, or it's not.
I had to measure a washing machine recently to find out if it would fit. I measured edge-to-edge, and by that I mean the actual left edge to the actual right edge. But you knew that already without me explaining.... because I said "edge to edge".