I suspect the 'You'll never get another Morrowind' has more to do with the weirdness of the setting and the feeling of getting lost in a strange land, rather than the number of square miles the game technically consists of.
Also, https://imgur.com/favorite-map-size-comparison-skyrim-other-games-series-B7rBN
...though I suppose you could say that 3/7ths is technically a fraction.