Which magic schools should I choose for the late game? Or should I go for a specific artifact?

Thanks for the replay; I found the thread about counter-heroes and downloaded more replays. Basically, I did as shown in the video, sending golems to the rear, but I must have done something wrong later, and those golems were quickly destroyed. The Black Archdevil immediately switched to targeting them. Well, never mind. We'll keep trying. Sorry for the off-topic, I just started writing in this thread.

Added after 3 hours and 4 minutes
And I also wanted to know, what advice can you give when playing as Razazak? Or in general, when playing as mages. Well, I understand that obsidian golems should be held back until the end of the battle, especially against Helmar, who likes to cast spells and other magic. And I should bring in steel golems more often. What else?