Depends on the time period. During the middle ages - uh... actually... I think never. The mongols and the turks were the only invaders from outside that are worth mentioning, I think, and after they left the borders were largely unchanged. I know what you're getting at, but here is why rogues and monsters don't solve our issues: They turn the game into a PvE game, making players even LESS inclined to fight each other. We would make the exact thing we want to strengthen even less appealing.
The problem, as I see it, is that without a certain element of randomness an island
will eventually develop a stable power structure, and these structures are bad for the game by limiting possibility, discouraging turnover in positions of power, and becoming ultimately exclusionary over the long-term. Without some sort of something to occasionally upset existing power structures and keep things from getting too settled they, well,
get too settled.When there are no (or few) established power structures and anything seems possible (post-Invasion, at the opening of Dwilight, etc.), the game is fresh and fun and engaging and everyone is inspired and excited. When opportunities appear limited and many realms are dominated by cliques of old-guard players who aren't interested in fresh perspectives from young upstarts, the game gets stale and boring and often feels exclusionary to players who aren't in the old guard.
I understand your hesitation to introduce PvE elements. Maybe there's another way to keep things from getting too settled? Or maybe we can experiment with whether your fear will be born out. Beluaterra would be a great place to test the rogue-spawn theory. If we do it, and Beluaterra experiences a surge of interest and an uptick in interaction, you'll have your answer.
