Whoah, I totally support the Burn Viper boss idea for the southern swamp, whenever I'm doing a flamming dungeon, that's the one where I always play purist except for bet on boss because of how easy it is.
Also the thief needs a little a hell of a buff, I don't know about you guys, but I hate the Slime pit. Can't do it with the thief, but I accidentally did a purist fighter run that I had a really easy time with.
Could we list the dungeons that the thief has a lot of trouble with? Maybe that way it's easier to approach this.
Slime pit, Namtar's lair, and Demonic library for me. I think the thief can't deal with physical resist monster as well as the other classes? Maybe his first strike against a full health monster should have some degree of penetration?