Camus or Rein

Rein, Xander functions more or less as a red Camus anyway and your team would be more flexible since youd have 2 range attacks and 2 melee

Reinhardt might be better to replace Mathilda due to the fact you have zero magic damage in that team, while Camus would be better if you have a Cecilia allowing him to basically be her pair-up bot.

Reinhardt is easily the most powerful mage in the game, able to plow through almost all red units with relative ease