My response to reading Legendary Sovereign is "this is a spectacularly lame ED"; I think that you're right that with a little tuning it might make a decent PP. That said, to my mind the problem with Legendary Sovereign is more basic. It's an ED that's about someone becoming a sovereign, not about someone being a sovereign. The idea behind LS appears to be that the PC in question is following a "return of the king" story line, and that the game ends at level 30 with them having become king and ruling a happy kingdom. There's nothing wrong with that storyline (although it doesn't feel very Epic to me), but it doesn't really work well for someone who wants to run a domain game, where the PC is actually acting as king for those levels.