Well, to be fair - Rastakhan was portayed as an abyssmal leader. Just think about it, during his reign the Zandalari Empire has fallen to ruin so much that it only controlled one third of their island and had no substantial holdings elsewhere. To make things worse, Rastakhan seemed completely oblivious to the threats to his people - he didn't know or care that the Blood Trolls were on the move or that the Sethrak rose up in Vol'dun or even that his own advisors (Jakra'zet, Zul, Yazma) were plotting against him.