Yeh, I think in isolation it might not be. I just know as an ENFP it can feel like an observational function almost. There seems to be total awareness of when I don't know things and where the ambiguities are. There isn't really much guess work or subjectivity at all, because everything needs to be contextual, and every situation is a new context. Direct comparisons to previous situations, like many types do to decide what something means or is, aren't really used that much. It's like read each one on its merit and if it is something completely new, adapt your brain to the situation, and understand this new thing.
Another thing we noted in one of the other threads is Fi appears to only have a few set values, the rest is interpretation. The values seem to be along the lines of, "don't cause harm to people", and "don't restrict the freedom of people or harm their ability to reach their potential". There can be a significant difference between what people perceive as doing these things though, which is where some subjectivity may lie.
Fi is very admirable. It has enriched my life, it has been more out of necessity that have to use some of the other cognitive functions. If I'm Fi dom INFP, it is unlikely that it won't be a significant part of my life again soon.
honestly Fi is not so well developed for me. It is a big gaping hole of scariness in there that I wall in with Ne/Te. It lives underneath and I share it with those I trust but it is such a gaping, poorly protected weak spot that I dont always trust it and I struggle to protect it.
I would say that, Fi is great but similarly I tend to have it protected with Te, mine feels like a weak spot aswell, I think its good to have a sensitive side, it is our humanity truly.