One important thing to consider about the Weylan is that they are fundamentally a peaceful people. The Albion designed them to be dangerous in battle but to crave peace above all else. That makes them some of the most heavily-armed pacifists in the known galaxy. And it makes Arkadia one of the toughest nuts to crack out there, though that did not stop the Shang from trying during The War. But the biggest reason the Weylan have survived all these years is because they are good neighbors. Many races have built colonies in the surviving habitable systems surrounding them, and they are the heart of a region of calm inside the devastated region of space the Albion once ruled. Most of the other races trust them. That is a very important thing.