The devs introduced two new high level allies, Princess Eli, which gives an exp bonus, and The Huntress, which offers an attack bonus. Hope this helps.
For Princess Eli's bonus, you don't HAVE to be using her to get the bonus. Just buy her, use ally books to upgrade her skills, and keep her in the bank while you use a more powerful ally.
Huntress' damage aura is not "passive". Overall, EP is still the best ally to use on a normal basis. Princess Eli is worth buying for the passive bonus, just shouldn't be used during battle.
For Princess Eli's bonus, you don't HAVE to be using her to get the bonus. Just buy her, use ally books to upgrade her skills, and keep her in the bank while you use a more powerful ally.