From some of the posts made in the Fi, Ti and INxP threads, it seems to me that being a strong user of a certain function by itself is neither good or bad since it mainly indicates preference, not skill in applying the said function.
Please be patient now as I try to make an analogy
Let's say there is a tennis player who is naturally tall and has a strong right arm. As such, he has a powerful serve. Now, if he just works on his serve and puts it into play a high percentage of the time, he's going to win a lot of points and matches. He might be too one-dimensional to be world number one or win Grand Slams, but he will still be a good tennis player. Yes, he could work on other portions of his game like groundstrokes and volleying, but his serve will still be the main weapon that he depends on.
Now let's take another player who is not tall and not as strong, but has great foot speed and court coverage. Again, he can work on his serve of course but he will never be as good as the big serve-dom Would you expect the coach to tell him to stop trying to run around but instead to go hit the gym and build up his arm strength?
I guess what I'm trying to say is that, while it might be optimal to be an all-round player, not everyone can be a Federer or Nadal. Is working on your strengths a better way to success than trying to improve your weaknesses? If you could only choose one, which would it be? Not really looking for a definite answer, but would love to hear others' thoughts.