Currently doing Chapter 11 Conquest. Tricky, but it is all about positionning (and abusing units with high Defense). Ironically, Silas is a better tank than Effie, thanks to good growths (he has 16 Defense, whereas she has 14+2), and with Effie supporting him in a Defensive stance, he is basically invulnerable (especially with the Nohr Blade, which grants +3 Defense). Without him I don't know how I would have dealt with the ninjas (well, there is Camilla, but I decided to not use her at all for this chapter).
I am shamelessly abusing the fact that the boss of this chapter can be healed to level-up units. Mozu needed the weapon experience anyway, since I reclassed her into an archer.
... Wait.
At a decent level on top of that? Didn't expect that. Oh yes. That being said, his strenght is kinda low.