When speaking of the Roman empire, the major historian of the period was Theodor Mommsen who wrote his work on the history of Rome in the 19th century. You use the term bias, but while certainly important, you have to remember that it is basically ubiquitous in history, from ancient to modern historians. In the context of Mommsen, he wrote his work during the formation of the German empire, and because of that pushed a "defense of empire" (which is a huge generalization).

Nowadays, we have moved past that idea and look more into the effects of empire to the common person, and from using primary sources like "The Golden Ass" we can tell that life wasn't pretty for the average Joe. When I took undergrad Roman history courses, it focused on the impact of empire on the lower classes, because too often the primary sources are from upper class citizens who did not have to same difficulties nor outlook that lower orders would. In that sense, we got a more "critical" look into the Roman empire. But even that is disingenuous, because is it critical compared to modern standards? Sure, but it is the premodern world and doing those kinds of comparisons to now are unfair.

Sources (apart from classes):

Pre-Industrial Societies: Anatomy of the Pre-Modern World--Patricia Crone

Why is Communism or Anarchism a bias? Liberalism or Conservatism would be a bias too, no?