It seems that sovereigns don't have enough stat points to be of much use in the late game, but if we give them more stat points then they become too powerful in the early game.
So here's my suggestion: tiered leveling.
At tier 1, levels 1-3, sovereigns earn 1 stat point to spend on their skills, just like the current system.
At tier 2, levels 4-6, they earn 2 stat points.
At levels 7-10, they earn 3 stat points.
And so on.