That's a pretty good synopsis, but you forgot a couple of things, the
effect of wavemaking drag (and the attendant "theoretical hull speed")
and the effect of cross section shap.

While we can argue whether the standard calculation (1.34 x square root
of the waterline length) applies to kayaks, there is no debate that
wavemaking drag becomes the major source of drag on all kayaks at some
speed. The shorter the boat, the the lower the speed at which it becomes
an important factor. With short recreational boats, this can become a
factor at speeds as low as 3 MPH.

As for cross section shape, a cylindrical hull has the least surface
area for a given amount of displacement and therefore the lowest surface
drag. A square cross section hull has the most surface area and drag.
Most kayaks are somewhere in-between these extremes.