Right. I'm probably not going to tell you something that you haven't throught of, but I find that Bible criticism fails because it accepts Descartes' premise that knowledge begins with doubt rather than Augustine's's premise that knowledge begins with faith. Especially when unfettered by a faith community's authority, Biblical scholars tend to treat Scripture like other ancient documents. This won't do. I seem to recall a story about Maimonides. that he almost reasoned himself out of faith. This seems to happen to Bible scholars. I once talked to Father Raymond Collins and he seemed to find some GLEE in telling me that "Mark" probably didn't exist!
I disagree. There is no reason Isaiah can't be studied using the same methods one would use to study the Iliad. But we need to understand that the conclusions of any such analysis are speculative, and that they don't change the meaning or significance of the scripture.