I've survived grand nocturne as all of the above plenty of times.

The main thing you need to factor in is that, in general, as a dumb character, time is not on your side. The phantasmal killer probably will get stronger and stronger as you fight it because you can't make mental saves for crap. In a lot of cases your best survival option involves throwing caution to the wind and pouring out all the damage you can as fast as possible.

For high int characters (most necromancers and transmuters, for example), the opposite is true; over time, your high mental stats will tend to beat the killer down and make it weaker. Your smartest option as a necromancer often could be something like, cast vampiric touch on something that isn't the phantasmal killer to heal yourself and play for time.

Conjurers are a definitely little more dicey, in that human/half-elf/half-drow conjurers don't have a terribly high int. A 23 int 20 wis (human trans) is a lot better off than a 20 int 20 wis (human conjurer). That being said, much like orcs, conjurers do specifically have an edge option to help deal with this kind of situation if it's a big problem for them. (Force of Personality.)

I think conjurers with an angel or demon bound take it in the pants the worst here, even though they're most likely the most dangerous conjurer setup for the bard to attack. While archons are clearly superior, I don't think devils are quite as useless for this situation as you do.