First, here is the element of Postmodern discourse I'm talking about:
https://en.m.wikipedia.org/wiki/Deconstruction
Second, my complaint is that it's not even considered as a possibility that Tacitus is telling the truth. In relation to The Annals (a public document concerning public affairs thousands of contemporaries would have had firsthand experiences of) do you really think it's a forgery? Or do you really think Tacitus is so biased he can't record history accurately? The idea that someone becomes so corrupted by their interests (especially race and class) that they cant be objective is a uniquely postmodern idea. The Enlightenment was premised on the idea that objective rationality was accessible to all.
Further, we can test your hypothesis about the Renaissance. The Renaissance writers read Tacitus, and when they mention him, they treat his works like a complete and unmitigated factual account. Also, Tacitus is not engaged in rhetoric. That's the point. He's writing history, not philosophy.