Future expansions.

This is actually a very important point. Your proposed option would allow the Academy to fill the mana bar quite quickly (at least by splitting into single units with high initiative to defend in the early game). I believe my version is more balanced and actually suitable for wizards; it turns out to be a kind of magical vampirism (in relation to enemies) and empathy (through their own actions). Imagine at least a battle between the Academy and the Sanctuary in the early stages. The mana bar would be filled during moments when heroes cast spells, Nagas use "Honor," "Waves of Renewal," and "Spiritual Bond," and wizard troops use their magical skills. In my opinion, this is something that really fits the spirit of the Academy, and it doesn't unbalance the game.