Necropolis – “Forward and Inward” [Campaign 2, Mission 2]

In short, the 3D action game's core is this: successfully complete all trials, defeat Kirill, and head to the "Stronghold." I played the mission as carefully as possible, but no matter how much I protected my army, Kirill still managed to eliminate about 20 ghosts in the final battle. I thought, "Okay, whatever. It's just the last battle." But then I get teleported to the "Stronghold," and there are... 43 Cerberuses, 10 Hellhounds, 63 Succubi (sic!), 145 Fanatics, and a level 17 hero actively using magic. In my opinion, it's impossible to defeat that many enemies while being bombarded with chain lightning and rings of cold, even if there were no losses throughout the entire mission (75 Ghouls, 90 Ghosts, and 23 Skeletons). Esteemed experts, could it be that I did something wrong?