I did manage to champion the Mage's path but I had to blow a ton of orbs honing magic to have enough to finish the boss rush.
The Knight's path I thought was pretty tough in comparison. I finished it, but only got expert on the boss rush. Not sure it's worth trying again and I had to spend like 2 mithril to finish the last couple bosses. Seem like these are all about honing now to have enough damage to finish the bosses.