As mentioned in previous posts, the most potent sources of damage for Thaumaturge are its DoTs - Bio II, Dia II, and Poison II. Damage on NMs and higher level mobs in general is severely scaled down. A small number of damage sources in the game, most notably DoTs, do not scale down, however, and becomes very strong sources of damage the harder the mob you're facing. With all 3 THM debuffs on, you can expect about 200 damage a tick (3 second interval).
Source: http://kanican.livejournal.com/53093.html


I use all three on CON/THM, and occasionally lower classes. I did my entire GLA36 Class Quest with 15 STR and DEX. I didn't want to reallocate points from DoM, so I used poison2/bio2/dia2 and watched the Quest mobs' HP whither in seconds.