I wonder how the archeologists came out with the fact that what is drawn is drawn at scale.

Proper relative scale in drawings is a (relatively new invention. When you look at ancient drawings, they are often out of scale for ego reasons (Egiptian art for instance), or just nobody cared (European Middle-Age).

We sure have other cases where the scale is more or less correct (Romans) but without more references than localized paintings I have doubts about teh ability to draw conclusions.