I usually powerlevel so far, that by the time i get to the final dungeon (its near the end of my to-do for every life, well after pheonix tower), i can breeze through. If you're playing Xiania, charged armor with a good int will trivialize everything short of lethice. Blind is also pretty much mandatory for subjectively difficult fights regardless of your playstyle. The key to getting through quickly is to know when to whitefire, and when to arouse. Bye bye Lethice, i'll think of you with indifference when i fight Merae.
meh
Protip: Keep your min lust at your black magic threshold, and spare no effort for raising your lust resistance as high as it will go.