Black Sister Champion compared to her leader counterpart.
Compared to the Black Sister Leader, you pay 18 pts for:
1 ST, 1 LD, 1 WD, 1 AR, secondary attack, commanding presence and loose 1 Def.
I think this is unique in the game where you actually loose a stat going from leader to champion. Given how low their AR already is for such a costly unit, i highly doubt that the AR gain compensate for the lost defense. You probably also noticed that she didn't even gain CC.
Imho she should get +1CC and keep -7 Defense like the leader.
Now Let's take a look at the Blade Maiden Champion and her leader counter part.
Compared to the Blade maiden leader, you pay 25 pts for:
2 CC, 1 ST, 1 Ld, 1 AC (!), 1 WD, 1 AR, commanding presence
Note:keep in mind that all blade maidens have killing stroke, therefore being more deadly than the secondary attack of the black sister leader.