I think that Ni+Fe and Fi+Ne, a lot of times, will come to the same conclusions about things (centered around idealistic visions of how people should treat each other)- and a lot of characteristics which are often found in Fi descriptions (integrity, low tolerance for injustice, etc) are really more about these conclusions than they are about the process Fi uses to get there. So I think that Ni+Fe can come off like Fi if you’re referring to the idealistic end qualities usually associated with Fi- but the resemblance breaks down when you start comparing the processes used to get there.
Fi’ers process things in a different direction; they’re more mercurial in an immediate sense, they’re inclined to want to break off into abstract ‘feeling tones’ (or something) in the moment and Ni+Fe can impatient with that if it doesn’t seem germane to the situation/discussion at hand. It seems to me like introverted judgment/extraverted perception is more inclined to process the information immediately and point out abstract fragments that feel important; whereas introverted perception/extraverted judgment has a tendency to want to collect a very basic framework from others so that we can go off and process the information on our own. Too many abstract F fragments in-the-moment are just agitating to us, we like to break down ‘what’s wrong’ in isolation, but Ps find it agitating to not be able to iron them out right away? In that latter sense, Ni+Fe does not resemble Fi.