I just now noticed from many character portrayals in movies, with comparison to real persons I know (and some serious thought) that P people are sometimes so damned intense they would kick J people ass with their speed of action - what some would call determinedness without knowing it better.
The movie that made me bounce this idea was Collateral, with Tom Cruise as the hit man. No I'm not the kind of person who sees a movie and believes in it. The movie rather made me reflect on the P people I know.
Once I thought about it I think I realize it. P person in the flow can make such instant 180 degree turns on demand that it can make anyone's head dizzy.
Then again, that what would be the work of determinedness for a J person, would not be so much that for the P person. He/she might not think all the time about the determinedness part (I can tell).
P person's flow is knowing the goal and keeping it cool, and just doing their thing. THe next thing to do comes after the first when they've done it. No need to schedule it.
So how I feel is that P is just not an incapable version of J, but that the capabilities manifest in a different ways.