If what they want is for archers not to destroy them in some shots, they could do what the battering rams do: “Make them receive 40% more melee damage”*.
The patch says it will increase the cost of the mounted samurai by +10, so CHECK.
As I understand it, this is OP because it has a bug that makes the attack boost larger than intended.
According to the patch notes, they’re going to fix it, so CHECK.
So let’s see. As far as I know, the Sengoku Mounted Samurai can already crush a value-equivalent combo of Spearmen and Crossbowmen. Yeah, that means it can straight-up cut down an army with a 2.4x numerical advantage that is supposed to be its hard counter.