At the Dawn, there were basically two cultural centers – Dragon Pass (also known as the Theyalans or the Unity Council) and the Peloria lowlands ruled by the Horse Lords.The Theyalans had a tradition of “realistic” art thanks to the Silver Age heroes called the Architect and the Artist (both of whom were active in Kethaela). Moreover, they had access to dwarf crafters, dragonewts and elves. And to surviving pre-Time relics. It followed geometric patterns of proportion and composition, and mortals and gods alike were depicted nude. This “Theyalan style” got spread all over the place, but also was probably really diverse. Individual artists did things in individual ways.
Meanwhile in Peloria, you start with court art that is intended to appeal to the Sons of the Sun. Lots of gold, horses, sun disks, etc. And it contrasts with Theyalan art by not being realistic or naturalistic. So very formal, very precise and almost abstracted at times.
When Dara Happa is formed, the new empire takes some of the ideas of the Theyalans and starts making sculptures of important gods and rulers (who are the same thing).
And they look at the Gods Wall for style. Because of course there are Pre-Dawn relics. Just like in Dragon Pass – we have relics from ancient times. Broken statues of unknown gods.
We also start getting more and more concentrated wealth in the later First Age. Temples spend substantial resources commissioning artists.
By the 3rd century, the Dara Happan Empire and the High Council were in contact with each other and began to influence each other. The Theyalan Orlanth was identified with the Dara Happan Umatum and Rebellus Terminus, and Yelm with the Theyalan Emperor. Once the Dara Happan Empire joined the High Council of the Lands of Genertela in the later 4th century, this influence became pervasive and the mythologies were fused.This also influenced art, as artisan went among Dragon Pass to Dorastor to Dara Happa. A rich Yelm temple might hire artists, only for them to later work for a Heortling king or Orlanth temple. This results in a cross-pollination of symbols and style from Ralios to the Redlands, Peloria, Dragon Pass, and Maniria. Regional differences, but also common influences. The later First Age is a shared language of mythology, art, and culture.