And I'll repeat the criterion (and not my criterion) for judging a scholar in the field which I believe is actually the Wikipedia criterion.  It is very simple.  Savory has written dozens of articles with regards to Safavid history  in peer reviewed journals, he has written books that are cited by scholars on the subject and furthermore he is the one that wrote most of the Safavid related articles in Iranica, Encyclopedia of Islam and Cambridge history of Iran and etc...  So no, all historians (and Tapper is not a historian) do not have equal weight when there is a contradiction.  For example Minorsky and Savory have less weight on Achaemenid Iran and Briant and Shahbazi and Frye would be better.  On Sassanid Iran, it is Frye, Daryaee, Christensen (although a bit out-dated now) and others.  On Shadadids that would be Minorsky and not for example Savory.  The criterion for judging is objective.  The number of articles, books and etc. written by the author on the specific subject.  But in case of a contradiction, I do not necessarily go with the scholar who has more weight, and I try to first examine the primary source.  In this case, the 'Alem Araay Abbassi I believe explains how Esmail I was crowned and what he said.