The fact that he made 3 grand finals in a row notwithstanding, he only won one of those, in his debut year. That was 2002. Ever since then, he has tread water in a pool of shit, hopping from one responsibility to the next, whether it be club or representative level, and failing at every single one. And don't bring up his stint as the Kangaroos coach, that was all the unified skill of the players.
Why is it then, that these talent bankrupt clubs (Cronulla 2007-2010, Parramatta 2013, Canberra 2014) put so much stock in those first 3 years of his career? That is ancient history by today's standards. His name always manages to find its way into the headlines, whether be over one of his signature whinges or something else, while actual amazing coaches like Hasler, Bennett and Bellamy with a proven pedigree get on with the job without making a big song and dance in the press over every little thing.
The only other challenger I could think of for the most overrated coach of the modern era would be Tim Sheens. Coaches who have had more than their fair share of chances, come up naught and continue to get them.