You can get outside Verdistis by tossing a teleporter out the front gate (or by hex editing
).EASTEREGGS and RUNE manuscripts
(unfortunately many of the screenshot links are broken)
I don't recall Larian ever stating that they cut back on the size of Verdistis, but (IIRC from checking it out years ago) it does seem a little more detailed than necessary if it was only background to be seen from inside the city walls (though they could have used old elements from when they were designing areas in Rivertown or the Dark Forest, or something).
Larian did say that the thought the Dark Forest was too large when play testing the game, so blocked off the south east corner with a river.