Balor way too hard

The Balor presumably takes damage from lawfully-aligned weapons, too.

 

I just repeated this fight in a second playthrough with different characters and chewed the Balor up with just two fighters. The extra weapon feats the fighter class gives you makes all the difference. Had a 3 lvl Pal/8th lvl Fighter and dualed my original straight class barbarian to a 5 lvl barb/6th lvl fighter. Threw Greater Heroism on my Bar/Fighter with Haste on both, and the two took the Balor and another summoned Balor down fast using just the +1 Holy Longsword and Frostbrand. Not even a contest!