I would respond that you'd be correct IF Bolton, Pompea, Mulvaney, etc. would respond to subpoena's or if they would release the notes that people like Ambassador Taylor had made on these topics then you'd be correct. They're not doing so.
It may be that I misstated the absence of precedent in process. I believe precedent is cited in argument and in fact if it is convenient for those pursuing the impeachment. But again, that is the argument to be laid before the people as justification:
"They did it too."
It's important to me that we as Hornfans not fall into that trap. How would we conduct the hearings? Do we have a standard that is elevated beyond what we are witnessing? It would seem we could come to an agreement in general on that front. In other words, are we political animals or truth-seekers?