Right now, the Champion and Wizard King are noticeably weaker compared to the Dragon Lord and Giant King, especially in multiplayer — and that feels disappointing.
The Champion is in a slightly better spot, since their Commander skills boost the entire army, which is particularly useful for evolving units. But the Wizard King feels way too weak. I had to try really hard just to make a build with him work at all — and I know that the Giant King would have done the same thing much better.
So, I suggest at least giving them a stronger economic start to compensate.
For example, the Champion could start with an store house in their capital. On the one hand, they specialize in food production, but on the other hand, they usually don't want to build store house— their farm provinces give more food, and the store house building is less effective by comparison.
The Wizard King could start with a shrine and +50 mana. Since they rely more on spells than other rulers, this would help their early game. Right now, when I start as a Wizard King, I have only 50 mana in stock and 20 mana income. Summoning a unit costs 60 mana, and I also need mana for combat spells. So unless there's a free mana crystal on the map, it's often better to wait until turn 3 for the first fight — and that feels far too slow.
It won't solve the problem entirely, but I'm sure it's at least a small step in the right direction and doesn't require many resources to implement.