With this engine they can't make zones that size again with this resolution and the same number of unique artifacts.
In version 1 there were a lot of complaints about copy/pasta terrain. Especially the Black Shroud (all of it) and the cave systems in Thanalan. The devs did it that way because copy/pasta terrain uses a lot less system resource. So, they made the zones smaller, lower resolution but more unique.

There are gains and losses to this system:

Gain:
No more miles and miles of twisty, warren-like corridors like the Black Shroud (V1).
More unique landmarks (sea serpent skeleton in Outer La Noscea, bridge over the marsh in Lower Shroud).
No more seeing the same terrain configuration over and over again.

Loss:
No more wide open zones (Sagolii Desert would fit in the tiniest corner of Coerthas) for exploring.
No more grand vistas.
Lots more zone lines/loading screens
No more detailed textures.

My own personal opinion? I preferred the old zones. But I understand why they did what they did and the new zones were certainly impressive the first time you saw them.