One Freemason who is also a historian on the topic (and rather renowned) is Helmut Reinalter, who was a professor at the university I am currently studying at. He mostly writes about history of ideas, with focus on freemasonry and enlightenment. Unfortunately I am not aware of English translations of his works, but if you can read German you shouldn't miss it. I didn't have the impression that Reinalter, as professional historian, had any problems regarding bias and such. He never hid the fact that he was a freemason himself, and always made clear which point of view his works represent. Of course it might be useful to get contrasting views from the outside, but to understand the historical development of the ideas of freemasonry Reinalter is perfect. This article by French historian Pierre-Yves Beaurepaire names some other influential academics researching Masonic history.

As for impartial historians, I'd go for scholars who do/did general research about the history of ideas, as it is pretty difficult to do comprehensive research on a topic like freemasonry without being involved. Maybe Foucault or Habermas could be of use for you in this context. I'd say a broad knowledge of philosophical schools and intellectual currents is the best way to get out of the "echo chamber" you mentioned.

Hello! I deal with Masonic history extensively, and I think its very important that you have asked this question to both us and r/freemasonry. You will definitely get very different answers. My question to you is, what aspect of Freemasonry are you interested in? Origins? European or American Freemasonry?

In any case, I definitely recommend signing up to the Journal of Research into Freemasonry and Fraternalism, where all the leading historians on the subject publish their work.