Interesting. The difference in finish , quality of workmanship.
The/a guild or "school" creating vessels was likely far removed from building construction in regards to pressure of time and production amount earlier , and rushed/pushed later? Or in caste.
Or as you mention , skill levels fell off.
Is it believed the same culture crafted both type/eras vessels?
And was there any overlap of teaching between the class of artistic craftsmen and common laborers and or slaves beyond basic instruction?
First glance would have the better vessel works remote , but local and separate from building assembly labor.
Or servants/apprentices doing the finish/grunt work on the building , and the vessels simply outsourced or acquired from another area and unrelated to any local craft..