(that dhar studying black magister in canon no one was in a hurry to depose and who was accepted back after he finished his research and proved noncorruption in the Felix and Gotrek novels has been brought up multiple times.)
He did not study Dhar, he studied Chaos, probably from the religious end of it, he also somehow managed to wield two winds and not go mad, the lucky bastard.
*not at all serious grumble*