Yeah, I agree that this theory doesn't negate the shadow theory. I think Te Si does come out as my shadow when stressed, which is why it is rather ugly/distorted (as most INFPs report).
Also, with Ti and Se, in this theory, it seems we use them simultaneously with Fi and Ne (?), which may make them harder to distinguish as individual functions. I've always seen it like a scale anyway....something like this:
Fi <-------> Ti
Ne <------> Se
Si <-------> Ni
Te <-------> Fe
So this is my initial take on it: an INFP will always prefer Fi, but Ti is the second introverted function choice, and they tend to work simultaneously. INFPs have an order to their values, and INTPs do make ethical evaluations. I suspect an INTP makes more subjective, ethical evaluations than a Fe-dom does.
However, when Si or Ni are engaged, there must be a focus to use them. For me that makes sense, because again, Si and Te tend to come out when I am stressed and they block out everything else. It's like melt-down prevention mode - Fi and Ne need a brief vacation.
I also have to make a conscious effort to use Fe and Ni, so they hog the focus when in use also. Fe tends to be at odds with Fi, so it's like I have to suck it up and just do it and ignore Fi telling me it's all total BS.