Let’s look back to when troop roles were first introduced:
This is a simple request: Corpse Mare is much more suited to the role of Warrior than to Generator. It generates 8 or so mana with each cast, but steals life—well over 20 in the end game. That makes it a passable tank, but a pretty awful mana generator.
Please consider making this change. Should not take a whole lot of dev time to discuss or implement!