Assuming favor chess samurai has FC slowness (as stated in the note), B>A but B is still balancable. It's basically an angel without the "frills" smashed with a rook, and angel is already a scary unit as is. The slowness serves to keep the unit in check and not just instantly cause a T1 checkmate. I don't want FC samurai in CEO as it skews the meta heavily toward paladins. I would intentionally overcost B for fear of it degenerating the meta if it were fairly costed, so 20/21 seems right for it.

Assuming it can be used on turn 1, B≫A (≫ is the "much greater than" symbol). T1 checkmate is broken.