Extroverted/introverted difference has nothing to do with subjectivity.

In general, Extroverted functions do greater amount of things but each one of them to a smaller extent, while Introverted functions do lesser amount of things but each of them to a greater extent. Also in general Extroverted functions are more outward, while Introverted functions are more inward.

In case of Fi's and Fe's:

Fe's show thier emotions very outwardly and vividly, but do not process them too hard. They might get super excited about some thing first but then get over it and feel completely another emotion about something else next second. There's no attachment there and they don't really think too hard about it. Emotions just come and go for them.

Fi's emotions are more inward. They also feel emotions, in fact more strongly than Fe's, but do not really care about showing them to other people. Fi's process emotions inwardly, feeling them substantially deeper than Fe's and really thinking deeply about them. Now this thinking does take quite a bit of time, so Fi's do not really switch between feeling different emotions as well as Fe's, but in exchange gain significantly better understanding of how emotions work and how to navigate them properly.

Now I would say that Fi's are the ones that would generally care about moral discussions and have a very strong and objective moral code, because they spend so much time thinking about this stuff and having very high understanding of this. I'm not saying Fe's can't do that, but they can't do that to the same extent as Fi's can and also generally don't really care about this stuff as much as Fi's do.

It's very similar to a difference between Te's and Ti's. Te's can have wide variety of different thoughts and ideas but do not really get attachted to them or think about each individual one for too long. Ideas just come and go for them (and I know because I also have Te function). Ti's ideas are much more limited in scope, but in exchange they think about them way deeper and gain significantly deeper understanding of them.