To make the allegation "you can't possibly know how common mastery of the Hebrew scriptures was among the rural poor in 1st century Palestine. It is conjecture." will require a bit more in the way of bona-fides then you have exhibited heretofore, as with the assessment of Hebrews. 

Biblical historians come in all forms, sizes, stripes, and opinions. And they communicate in learned journals, academic tomes, and popular paperbacks.

I personally would not adopt some theory put forth by a "biblical historian" without considering context, surveying contra opinions by other scholars, and recognizing that there is a lemming-like tendency in academic circles - where publishing is god - to all run for the cliff, leaving later generations to clean up the mess - e..g, the Q text.