A later castle age isn't ideal against Japanese because they can grab relics with Shinto priests.

Imported armor is a critical tech, but less so against Yumi who have slightly less damage.

The challenge using Javelins versus Yumi Ashigaru is that you will overkill a lot of Yumi.

With Sofas you deal with those Yumis pretty well if you can survive and get their armor upgrades as well eventually.

Once imported armor comes in, Yumi archers won't do any damage against sofas anymore. Imported armor gives sofas plus two melee and ranged armor, so they take significantly less damage from Yumi archers and TC fire.