I'd say slavery is less common in the later ages of Arcoscephale. A distant war of conquest brings less slaves than war with neighbours. Still, they probably use slaves for utilities sake. Slaves make the lives of the rich pleasant. Why abolish something like that. If you dislike how they are treated, treat your slaves good
I would say most dominions nations use slaves to some extent. Abolishment is a quite new invention, and has always (more or less) come in conflict with political interests of competitive rulers of the nation. If times are peaceful, culture and religion thriving, slavery mighht be questioned. But if the nation competes with other nations over land, wealth or other resources, a slavery that further political interests of the nations less likely to be questioned. Religion might be exception to this. Since faith does not need manual labour to prosper it can safely stand against slavery and inhuman treatment and actually benefit from it.
I dominions you might speculate that a nation with strong dominion and order probably is more likely to abolish slavery. Every one is a believer and everyone knows his place in society. If everyone is working properly, there is perhaps less need for slaves. On the other hand, slavery in an orderly dominion might be ordered by god and less likely to disappear. If priests of a centralized faith have a strong influence, part in competition with the temporal powers of the nation, things might look even brighter. Pythium for example might have a history of slavery, but if your dominion is benevolent it might be that the Theurgs are taking a stand against it.
So to answer the question on MA and LA Arco: Your priestesses are not very influential, but might well oppose slavery, depending on your god's dominion. The general populace is probably quite satisfied with the slaves they got. If you have a long period of peace you might imagine that slaves become luxury, since no new slaves are imported. With slaves increasing in price they might get treated better, get possibility to buy themselves free, and eventually slavery will become marginalized.
The sibyls might place a ban on slavery, also depending on the will of god.