It seems to me that the research is not objective enough. The sources you used seem to give information only from the Russian side. Sources from a different point of view should be consulted; let's remember that history is written in most cases by the ones who are, or were, in charge. Maybe for Russian history Catherine the Great was really the best monarch that ever lived, but for countries that surrounded Russia she was not.
My suggestion si to determine the characteristics of a great monarch then, based on those characteristics, compare Catherine the Great with other monarchs. In that way your arguments will be solid and won't lack of credibility.