I don't know anything about these random people's function order theories, but logically, would it not be different depending on the relative strengths of the four functions? (Beyond the Ti-Ne-Si-Fe basic order, that is)
No, because that is actually how the system works. There are degrees of preferring any dichotomy. The system is limited, in that mostly likely one can actually result in XXXX, if you answer the assessment 50/50. It's impossible to provide forced choices, because human beings are more complexed than either or questions.
For example, an INTP who has a weaker T (ie leaning towards INFP) would have Fi higher in the function order than one with a very strong T. An INTP with a weak P would have Te (and probably Ni) higher in the order than an INTP with a strong P. And so on. So I don't think there can really be one function order for all INTPs. Does this not make sense?
I understand your inquiry, however as Pgats points out, the principles are in place, and INTPs use Ti-Ne-Si-Fe. However, they do use all eight functions,and depending on how you believe those functons go in order per type, the other four can either follow the aforementioned, or be placed intermittenly between them.
As for your example, you compare a function (Fi) with a dichotomy (T), which is apple orange. To answer your queston, weakening of preference for one dichotomy simply means you will slide over to the alternate dichotomy. Thus, the less you prefer T, more you prefer F. Nevertheless, functions are not part of the assessment equation. It is why Socionics can continue to make their case as to the order of functions for introverts.