The P wouldn't neccesarily have open and expansive plotlines, moreso they'd be like RL Stine, where they just write off the top of their head, with limited preparation; their characters would have a life of their own and write themselves.
The J would tend to have detailed notes and have things planned out far in advance of actually writing the story itself. This actually tends to lead to more complex plotlines, rather than whot yeu'd suggested. The J will have better knowledge of the start, middle, and end, and whot they want to happen at each stage along the way, which also means they can set up 'surprises' to occur later on but be hinted at early in the storyline.
The P, however, will tend to have far more natural characters, that feel more alive and less like they're being forced into acting a pre-defined role; J writers have a bad habit of making a plotline and forcing characters to do whot's required by their plotline regardless of whether it makes sense for that character to do so or not. The P's are more likely to have character development and characters that practically think for themselves, and act consistently, but are unlikely to have structured, complex storylines for those characters to enact.