Sorry for this reply being so late.
Yes, the partition system is actually the new way ASA handles maps. WC no longer supports world composition.
https://devkit.studiowildcard.com/getting-started/creating-new-maps
As for your issue, this is a common problem. However, there is a work around!
When creating your landscape, set the scale to 1,1,1 (x,y,x)
Then after creating you can adjust your scale to be what you want.