My preference would be for the unit roster to be linked to what’s available at the Dojos and/or Shogunate. I think you could do one unit by default like your example, but it could be expanded by the special buildings. That would give more value to those buildings and give opponents the ability to deal a meaningful blow by destroying those buildings. Something similar could be done with a Chinese “general” and the Summer Palace wonder.
I don’t really see a need to be hung up on keeping them so historically specific. Daimyos were pretty common and could be more generic if they fill the hero role. Since they are such a powerful unit, I’d be hesitant to give them an immediate ransom respawn. The African style timed respawn could better moderate the power of Daimyos by making players wait for a cooldown to finish.
I should have linked that post to here since it’s related. I’ve expanded on the idea more in this post: