The Main Plane, or rather the deities who stand apart from it, were indeed the victors from epochs past. Yet aside from those who successfully ascended to deities, there were always a number of competitors before their ascension. Most of these opponents were killed by the deities, but there were always a few lucky ones who survived at that time. Although these beings may not have become deities, as long as they created Ancient Ruins Spaces and continued to survive, given their potential and strength, it is likely that they could give the deities a run for their money in a fight now.
However, these ancient beings did not have much concept of territory. Hence, many Ancient Ruins Spaces at that time were nominally ruled by demigods. And unless something threatened them, these ancient beings would not easily interact with outsiders.
