So how many ISTPs have you talked to IRL, who are so concerned about their families as Katniss is? And so readily respond to their needs as Katniss does?
Usually the ISTP gets criticized because no one in the family realizes they actually do care (same problem can occur with INTPs), and they don't like to remain emotionally engaged. Why? The natural expression of DETACHMENT.
Katniss is hyper-protective of her inner world and emotions, but she is not detached. She also has a large reservoir of anger constantly coming out, when people threaten her family or try to violate her wall. This anger actually resembles closely the behavior of INFJ females I know IRL. Is that an ISTP approach? No, they are usually just avoidant and don't as easily leap to anger. Compared it to Andrew Garfield's more ISTP version of Spiderman; detached, easy-going, even if elusive. Katniss can actually express her feelings when she wants; Parker can't do it, he doesn't really know how and isn't actually in touch with his feelings. I think also OVERstate the "idealist" aspect of things for INFJs; the ones I know might be idealistic in some ways and care about the people they love, but typically their sense of privacy is so strong that they don't put their emotions and values out there for everyone to see, nor do they LIKE being roped into things. To be more overt in their ideals like the E's are would put external obligations on them, and they typically avoid that. They can be more elusive, unless you are one of the few let into the inner circle.
So no, Katniss is NOT "so ISTP I can't even imagine there being a debate about it." Otherwise there would be no debate occurring. I still don't see anything you've said to address the big issue between attachment and detachment, and inner emotional awareness vs lack of it. On the surface, Kat is highly protective and withdraws, but she is not detached and oblivious, she's very canny and aware of the demands being placed on her, in intricate detail. ISTPs are typically not so nuanced in their awareness, they just refuse to be caged.
OK, so there is a degree of debate possible
To me, the things about Katniss that deviate from 'typical' ISTP thinking, feeling and behaviour, come from her being so damaged. Her father's death, her mother's subsequent emotional shutdown and the starvation that followed, really, deeply affected her. Her strength of feeling towards her family (especially her sister) and her need to be the provider and protector, comes from the deep seated fear and helplessness she suffered during those weeks after her father died. I would say she very much a phobic 6w5 filled with anxiety, in this case about losing control over her life (which includes survival, autonomy, and her family's safety). She also possess the 6's sense of loyalty, duty and dedication, as well as their compassion and courage.
I would also argue she's a very detached person. This does get complicated because
movie Katniss is much warmer and pleasant than the grumpier and colder
book Katniss - but to make it easier I'll stick to the book version. Katniss certainly feels deeply but she is often very distanced from her emotions - she actively pushes them aside on a regular basis and focuses on practical matters (like killing people in the games). When the PTSD gets worse, it becomes harder for her to do this, as well as when those selfless 6 sensibilities take over (like with Rue and Peeta). I also think she is bizarrely oblivious when it comes to interpersonal matters, in a way only a Thinker could be (not to say that all Thinkers are like this by any means). It's almost ridiculous how blind she is to the fact Peeta is attracted to her and how she manages to have no grasp of how people see her. To me there's no way a Feeler, whose realm of speciality is the interpersonal, could miss this stuff so completely, over and over again - least of all a INFJ. She is emotionally naive, yes, but she puts so little emphasis on emotional matters, both her own and others'. She's a practical person and that stuff is just not her priority.
To me she's obviously a ISTP because of her skill lies in being a brilliant practical improviser. She almost never plans what she's going to do, even when it comes to the games, nor does she think things through to their possible ends (like the trick with the berries). She just waits till she's in the situation and responses to the elements involved the best way she can; that's her skill - that's her genius. The far reaching elements, like the rebellion, don't have an immediate pull on her. She's rarely thinking about the overarching ideals; she's just busy dealing with the stuff that's right in front of her, one thing at a time. Even in
Mockingjay, she has to be dragged into the big picture stuff. While she agrees with the rebellion, she only becomes the Mockingjay in order to protect Peeta - she just uses it as a bargaining chip, not as a opportunity to change the world.
Hm, I actually identify quite a lot with Katniss' character. I'm not sure that means much type-wise, since movie characters are designed to identify with people, but all of her motivations and actions make perfect sense to me. Even her strong idealism is ruthlessly harnessed to reality.
Caring for your family in a very concrete, practical way is a very ISTP thing to do. It's true that we can come off as not caring because of not being very emotionally/verbally expressive, but at the same time, you'll see us actually doing things to improve the family's situation, if possible. I agree that her emotions are closer to the surface than most ISTPs, though. I could see her as an ISFP, actually. It's always hard to tell with fictional characters (as though typing real people wasn't hard enough!).
She does have an inner NFJ, which understandable with this being her opposing type - but these qualities have to be painstakingly dragged out of her against her will by others (and in very difficult circumstances). She not a natural idealist; she just wants her family to be safe and to be left alone.
