I agree, they were the primary spellcasters, the "secondary" were the eredar warlocks that came along hahahahaha.
I do consider them masters of guile, of course, in the war of the ancients there was not enough talk for them to use their natural skills hahahahaha. I think one example of manipulation at an epic level is Saidan Dathrohan, let's face it, having an entire organization of zealots who hate you kind do whatever you want, and not even suspect that there's something wrong with their leader, is not simple manipulation, it's a work of art. Also, making Sylvanas believe that Varimathras killed Balnazzar was also a very good act of manipulation, trickery and oscar-winning acting XD
Though I've noticed that Dreadlords do their best trickery when possessing someone (Balnazzar, Mal'Ganis), but, the standard RPG dreadlord doesn't have that ability, which is kinda weird.