I think that is a pretty good crack at it, archfly. That seems about right, with a bit more than I could remember. If I recall, and as you might expect, you can't just combine a very stiff material with a much more flexible material and get an average of the two, the more so when their elastic limits are different as well. The fibers just fight each other if used for the same purpose. In fishing rods, at least, if used in different directions, one or the other is more or less useless. Yes, there was way more attempted engineering to it than that, but I think that's what it boiled down to--a solution with out a problem, or a solution that made a problem more of a problem.
There. To the extent you or I are wrong, that's good, too and maybe we'll get some more specific answers.