Of course bias can vary, but I think most of the professors you ask would say they are being unbiased, or they are calibrating their bias to counteract their typical student's previous educational bias. After all, you were taught history through high school, but in a state-approved curriculum taught by overworked teachers.

As far as critical tools, which ones are you thinking of? Are you thinking of traditionally-leftist tools like investigations into power relationships? What do you think of as a value-neutral critical tool?

You seem to have an idea of what differentiated the good classes from the bad. I'm not disagreeing that some classes are bad, I'm focusing on the value the good ones can give. A bad engineering class, by analogy, teaches about a subject of little practical interest AND teaches it at a slow pace. Bad classes happen across disciplines.

And I admit I am probably speaking from a lot of hindsight. I took a couple good classes in college, and since then have read a ton of academic's blogs and semi-popular articles, and it has taken a while for things to "click" and for me to be able to say I can clearly analyze/criticize an editorial about history at a direct and meta-level the way I'm saying this education helps one do.

You're right, for instance, that in college you probably won't get an aggressive defense of imperialism to contrast with its criticisms, even though that might be useful to understanding it. But that's because an overwhelming majority of academics consider it to be such a clearly wretched, even evil, that they see no value in teaching it. It's just how we rarely see a serious analysis of abolition vs. slavery, because come on right?

On slavery, academia and the mainstream are clearly in sync. On Imperialism? Maybe not as much, especially given the blurry question of "what is modern imperialism?" (is it the IMF; is it NAFTA; is it Iraq?). But many academics are striving to make their classes the antidote to a naive narrative of American history that goes: "Columbus discovered America, immigrants came and civilized the Indians, won the southwest in glorious battle against corrupt Mexico, then their nation reluctantly accepted the role of world peacekeeper ushering in our golden age, and triumphed over communism".