I would like to support Winnihym idea. It seems good.
Even though technically you don't get less know across the world when your champions level up, so thats a minor point.
Maybe one could make Experience gain global meaning any experience earned by anyone will apply to everybody. That means commanders sitting in a city will level up as well as everyone else. And your sovereign will be always on top. Because he was the first hero.
(That would definately mean that Tutelage would be OP but that could be reworked.)
I'm just throwing this out here.