Nice Korvin.
Following is a rough description of my first game playing Yomi (Single Player):
I trained my first Oni King on the 2nd turn and made him my prophet. After building a reasonable army of bakemono archers and bandit infantry with small flanking groups of poison spitting, flame throwing Kuro-Oni, this initial force cleared indy provinces easily and the prophetized Oni King reinforced the ranks by reanimating armored souless as they advanced. As the gold income began to rise, more Oni-Kings followed and were equipped with horror helmets and bracers of protection (since early on that was all I could afford). I had them cast 1 or 2 buffing spells and sent them into the fray. AI troops rout quickly when the kings enter the battle.
I initially have used the old sorcerers for research and forging simple items with multiple castings of reanimation at times when I needed to quickly amass a wall of fodder for absorbing arrows. Mixing small squads of the cold Ao-Oni in with the front lines was quite effective in adding some serious punch against some of the heavy armored enemies. The undead fodder also helped to absorb banishment bombardments.
The game is still in progress and not a sure win by a long shot. Research is very slow and I now border 5 AI's, one of which I have nearly defeated (Ermor).
I can see where it would be a rough pick for competitive multiplayer. I bet however that someone will come up with a healthy strategy to make it shine.
I like most of your suggestions, but I would prefer to see the small Ko-Oni retain their small stature, but reduced in price. As it is I train stealthy prot 11 bandits for 9gp instead of the 12gp banishable prot 3 Ko-Oni. I guess the "end of weakness" spell may make them more appealing, but I still lack about 290 research points before I can try it out.