I think a J hero would be more effective than a P hero. P's stereotypically don't think things through.
Not if its an IxxP! - Usually though, ISTPs seem to be backup, like that mechanic that can fix ANYTHING. (Cid from FFVII is a good example, he could be an ESTP, though.)
Seems that NTJs or just TJs are common main villains because of some overpowering moral inside them. an ENTJ can go berzerk if they watch what was important to them die. If they get 'stuck' in steamroller mode, then you have a good villain. Same goes for INTJs, but those are more of the shadowy kind of villain. Like Dracula.
The reason, I think, that villains are usually Js is that they have an internal vision that they have been planning for a long time and then some asshole P comes along with these frivolous morals and tries to ruin your years of hard work.
How would you like it if you spent many years of your life planning, saving up for, and building a house with your own hands just to see some douchebag ENTP try and buy the lot and demolish the house so he can make some Chuck-E-Cheese or something?
The main villain is portrayed as being moral-less, but they generally have some internal moral that overrides the others. Like their family being murder or something.
Ps don't make good villains because they either sulk and do nothing, or run around smelling roses. A good villain has to be a hard worker, otherwise he's just one of the villains cronies (identity-less Clone Trooper number 23950716 anyone?
).
Ps are good heroes because in stories, the hero generally just responds to things, their plan is rarely far-reaching. They do the job in front of them and somehow it ends up saving the world. You can't really plan to save the world unless you're the INTJ 'villain' in that one movie with that one guy with that one blue skin with that one epic power of blue-ness.
Apparently the comics were better according to all the longtime fans.
Lastly, Js just have the stance for villainy. A J looks better as a villain on stage, with their piercing gaze.