Heh ... I kind of (almost) think that Champions in Elemental should rip from FFH and slowly gain Experience points until they reach level 10 
(fighting battles helps speed this along of course)
And meanwhile, if ALL sovereigns started off at level 5 (you build them at level 1 and "level" them in the Leader build screen for 4 lvl upgrades) ... and then they quickly gain exp till level 10 ... and slowly gain exp till level 15.
All new successor sovereigns (if your Sovvie dies and a Child takes over) would not get any free levels, but would quickly gain exp till level 10 and slowly gain exp till level 15.
Combat and Quest exp can of course both speed this process up and (once cap is reached) go beyond experience cap.
Maybe certain Military and/or Educational buildings can slightly speed this process ... as well as train units up to level 3.