Plopping down Katie then dropping Nadia in front of her once things start to get hairy is quite a bit cheaper than Gellius plus a mage even before you factor in Reinforcements. It also puts out waaaaay more damage. Garania's been a helpful presence in my army but she should feel kinda embarrassed about being so close to Nadia in cost.
They were being sarcastic.
Anyway, I think you're missing the forest due to the trees again. Nadia isn't an anti-rush duelist but she's easily the top anti-swarm duelist. She's so good she can even survive being a contradiction in terms.