Do keep in mind that Kage dispels first, meaning he is always guaranteed to bypass defensive buffs. Seshat only has a chance to do that, and that’s if she has emblems invested. TBH I don’t really want to meet either of them. 
The 4% mana buff honestly won’t make a difference unless leveled up mana troops are equipped, that’s very endgame too. Smaller players who get lucky and get her, won’t see the difference until they have their purple mana troop. See: Optimal Mana Bonus Numbers for Every Mana Speed (Now including Ninja Heroes)