Wizard – “Haven” [Campaign 6, Mission 4]

That's exactly the problem – Isabelle's unit count seems to increase disproportionately to the number of castles she has.
But I have no choice, I'll try to develop her.
And the advice to focus on Paladins and Archons is good. Thanks! Because those are the only units I usually have left, while all the others are destroyed. :)