I am not going to get into the historical method argument with you.  We agree significantly but in some areas we disagree fundamentally and this is one of them  One of the worst things about most histories is that they are so dry that no one wants to read them.  History can be both good and informative, sadly it is often neither because of the dryness of most historical scholarship.  What you call editorializing is no more than a judgment call within an interpretation.  I chose the example I did as just that, an example.  History is more than a dry recitation of names, dates, and places.  The judgment calls come into play when talking cause and effect.

My professors come from Duke, Rice, Virginia, Maryland, Wisconsin, University of Washington, Princeton, and Oxford (these are the most prominent influences).  They all pretty much agree in the writing style I've been taught.  Some are young and some are old so it's also across generational lines.  European scholars might be different, but I've not had too many from overseas.

I wasn't talking about making a case for or against why one side lost, only adjectives that call so and so “great” when it can be debated and is of no real significance to the content whether he was great or not.

I agree that "great" may be too subjective of a word to use (depending on the context) when one wants to provide an objective assessment.  I personally would be uncomfortable being a "cheerleader" for someone or something by the way I describe them, and I don't like hearing other papers which try to cheerlead values which are subjective.  But I do think there is some wiggle room  For example:Among Charlemagne's greatest feats was... (I think this is fine)Charlemagne was the greatest of the Carolingian rulers... (could be ok given support)Charlemagne's greatness was due to his... (this usage is suspect)

This is okay, but I would use "most important" or "more significant" or "noteworthy" feats etc....

The idea is to denote significance and importance without “singing praises” and cheer leading as skiguy said.

Instead of telling the reader he is the greatest, at least by adding "considered by many" this still leaves it open for the individual reader to judge.

I'm cutting hairs here a bit, but to be technical, it could be problematic to say "considered by many...".  To illustrate, it may be true that "many consider Hitler to be the greatest leader ever..." because a hundred people, a thousand may think this.  Nevermind the millions who don't think this.  But technically the original statement could be true.I personally don't mind some arguably subjective statements if they are inconsequential or not worth arguing about.  Even a statement like "Charlemagne's most noteworthy accomplishment..." entails some level of subjectivity because we don't have a quantifiable or objective standard of what connotes "noteworthiness".  However, we're not robots, so we understand that the writer is putting forth an educated view based on his research.  We trust his research, we trust the publisher who put his research into print, and so forth.  True, the writer inserts his own opinions about Charlemagne's career, but hopefully they're backed up by facts that correspond to our own subjective dispositions.  In the end I don't think it's an exact science and there can always be some debate about whether a writer is objective enough.