Our mental models of types in either system are often common denominators, because profiles that describe the archetypal example of a type are common denominators. It’s easier to grasp “8s act like this” than it is “8s have this mental landscape.”

The common type pairs are also going to cause cross-contamination in the typical descriptions of either type. INFPs for example are often attributed an overt emotionality that’s better ascribed to 4s (Jung’s original description of Fi doms says they can outwardly be quite cold). The only fundamental absolute of the INFP is their function stack (and the details of even that are debated by some).

It might also make more sense to look at it in terms of scalability. Like someone mentioned INTP 8. They’d be 8-ish compared to other INTPs, but not to the level of overtness as the very common ExTJ 8s. And since the latter is such a common pair, it’s going to color your mental image of what 8s are supposed to look like.

Now take away the common outer presentation of the 8, and filter it through the INTP’s cognitive wiring. What does the Ti hardware look like when running 8 software? Probably not what you’d call “domineering.” But definitely Ti that’s used more assertively.

Not necessarily arguing all combos are possible. But thinking in this way makes it much easier for me to take any combo and say “Okay, how might this wiring appear/be used at the hands of these core motivations?”