Writing in the union's newsletter, The Specialist, Mr Powell said no DHB performed well in a survey of members last year of how well DHBs had implemented the Government's clinical leadership policy, known as In Good Hands.
Southland and Otago ranked third-last and seventh-last respectively, having been considered separately because of the relatively recent merger.
Otago senior medical officers ranked their DHB "very low" for links between managers and health workers, and Mr Rousseau rated poorly for enabling strong clinical leadership.
"Unfortunately, the chief executive, while hard-working, has a propensity to get fixations on particular issues which makes achieving effective clinical leadership difficult," Mr Powell said in the article.
The other DHBs with low or poorly-ranked chief executives were Waitemata, Bay of Plenty, Whanganui, Hawkes Bay and Mid-Central.
Mr Rousseau declined to comment when contacted.
University of Otago health policy specialist Associate Prof Robin Gauld, who helped the union with the survey, said when contacted research showed top hospitals had doctors in strong leadership roles.
Surprisingly, little research had been carried out on clinical leadership, he said. Clinicians had to take responsibility and not everything could be blamed on management. Clinicians needed to seize opportunities to lead, he said.
The National Health Board planned to survey a wider group of health workers on clinical leadership.
