It's not that hard to break through the portal there. The real challenge is killing the rune guardian.

I have a question about the beginning of the Dungeon campaign. How can I defeat Helmar, who has the same stats as Varen and an army that far surpasses Varen's? He's the one who greets me at the entrance to the dungeon.
Option 1 - only with good magic, which Varen has no way of obtaining. I didn't offer him random magic, by the way...
Option 2 - if you take the first town and encounter the dwarf there. But that requires luck.
Option 3 - cheat.
I played on Recruit difficulty and didn't drag out the time: Varen started his journey into the dungeon before the month allotted for the siege was over. Logistics and boots were present.
I can agree that I'm a weak player, but I don't believe in miracles...
By the way, judging by the forum, the number of players who have completed the map and those who haven't is roughly equal...