You could probably find modern-day icon painters who said their works were to the glory of god.

The tour guides at these cathedrals we pay to go round spin the line of craftsmen doing it to the glory of god, with the hidden details that no-one would see etc. Do we have contemporary writings suggesting that they were merely wage slaves rather than workers subscribing to a delusion of the age ?

If you are arguing that the glory of god bit was just to keep the peasentry in awe then the craftsmen could have been in awe as well.