Although being a competent warrior was a requirement to be an arm-bearer, and thus an Ersta'la, these livings weren't exactly military leaders, Ersta'las were the most common titled members of the faiths, and tended to act as sort of city mayors, depending on a city's population, a certain number of Ersta'la would be sent out to live within the local solar temple, and that was pretty much it, they would oversee all sorts of things, but warfare wasn't exactly something common.
Most often, the danger were beasts and monsters, sometimes orcs or molochites but that was pretty much it, only the cities with the greatest population of worshippers of Watchful Undeviginti would ever be attacked during the time of Sanguine Undeviginti, other cities would just barricade themselves in and wait for it to pass, so apart from the Ersta'las that ruled such cities, few had any experience.
