Ah, I think I was misreading the rules. I thought since both boons were counted, that both dice were counted. That's my misunderstanding. Still, a hit of 10 would be pretty severe.
I've updated the description of the tie-breaker rules in the hopes of making it more clear.
And yes, 10 damage is a pretty tough hit, but it's a lot better than 14+! Also, don't forget abilities that can mitigate damage if you have them. Reducing a 10 to a 9 is a 10% reduction in damage, which is nothing to sneeze at.
The app has been released, which increases the "cost" of buying enemies that the dungeon generator "pays" to populate rooms, so you should also see a reduction in the number and total threat of enemies that you encounter in the dungeon, which should help as well.
Happy adventuring! I'd be interested to hear how it goes if you delve in with the new app.