Walkthrough for the "Tribes of the East" expansion.

Comrades, please advise. I'm currently finishing the last mission of the second campaign. All that's left is to capture that mega-evil magic castle and then defeat Alaric.
I apologize in advance if the question is silly :)
I understand that if I defeat the castle with Gothar, then it will take a very, very long time to get to Alaric from there. So, is it worth accumulating magic troops with a secondary hero and meeting Alaric with them (i.e., not with Gothar)? How is Alaric's army?
It's impossible to defeat the city with magic troops; they tear me apart like a rag after the third attempt...