You don't have to take my word for it. Sure, I think I have the right idea, but if you prefer more prevalent theories, you only have to look at Socionics, which matches dominant functions with J/P.
I know of Socionics, actually. But J/P are used to mean different things in Socionics than in MBTI. To be frank, J/P doesn't even exist natively in Socionics. That notation is the remnant of an ill-conceived attempt to "convert" the types to be recognizable to Western MBTI users. The correct Socionic notation is something like SEI or SLI for an Introverted Sensing type.
Isabel Myers created the J/P scale as a forth dichotomy to explain type. What Socionics calls "J/P" is actually the Jungian concept of rationality/irrationality (which is actually redundant in Socionics since knowing what the dominant function is tells you that in that system).
If you're equating J/P with Jungian rationality/irrationality, and hence talking about Socionics, then I most definitely agree that the descriptions in question describe what Socionics calls ISxps (that is, SxI's), more than ISxjs (xSIs).
My complaint is that I believe that MBTI J/P is NOT equivalent to Jungian rationality/irrationality the same way that the "converted" Socionics notation is.
Jungian rationality/irrationality is inherent in the functions themselves. N and S are irrational functions, T and F are rational functions. They're about how a person operates primarily, regardless of how they present themselves or interact with the world. MBTI J/P was based on how one presents themselves and interacts with the world, regardless of how they operate primarily. They're different concepts.