It's a 13" and is ~2.5x as heavy.

No it isn't. It's 1.08kg vs 1.23kg, or 13% heavier.

And indeed it's 13 inch but the dimensions are quite similar, there is a 0.8% difference in width (with the 11 inch being wider surprisingly, due to the bezels) and a 7% difference in height (11 inch being shorter). At its thickest point the 11 inch is. 33% thicker. In terms of volume the 13 inch isn't any bigger.

Just look up the specs.