Is this Jacob Hansen's version, or some other? Maybe it doesn't matter, because I see the same kinds of questions no matter whose version of "aggregate across multiple prophets" model I encounter. In theory, I think it is a good idea. Questions that I think tend to muddy the waters:
1) How do we determine who is and is not a prophet? Within a given tradition, there is usually consensus, but that also usually leaves some claims to prophethood (canonized scripture) out. We LDS accept Biblical and Book of Mormon figures as prophets, but reject Muhammad's. We accept Brigham Young through Russel M. Nelson, while rejecting Joseph Smith III through Staci Cramm (presumptive). I think it is worth acknowledging that your choice of prophets to include and exclude will impact the conclusions you end up drawing.
2) Once you've decided who to include in your list of prophets, then you need to determine what they said. This gets particularly difficult the further back in history you go. Did Moses really say all those things that are attributed to him? What about the letters of Paul? Even as recently as Joseph Smith, we end up going round in circles trying to determine what Joseph Smith said versus what his contemporaries claim he said. A lot of the time when I see someone like Hansen promoting this model, there seems to be an underlying assumption that we can accurately recall across years and generations and millenia what prophets taught.
3) Then there is the ever present question of interpretation, which, like the previous point, becomes increasingly difficult across time and culture and language.
I think a "collective prophetic witness" type of model can be useful in getting at truth, but only if we are also willing to recognize where it will struggle.