Good question...they aren't. PS, sighted fire, a combination of, or shooting while doing flips is all just skill development.
However, the converse is not true. The other 2 may preclude being able to use the sighs. Should this be the case, the subject will need to have developed the skill of getting effective hits without them.
You developed the skill through mastery of sighted fire (unconscious competence) along with your index. By way of carryover (plus extensive competition and practice shooting very close targets), you also developed the skill of getting fast hits w/o a need for visual sight confirmation.
A more direct route to gain the skill of getting hits w/o the sights would be to add in deliberate PS training and practice. We already know what happens on each extreme. The average cop is on the extreme of minimal training and we see their dismal hit rates. You are on the extreme of many years and tens of thousands of rounds. The latter is unrealistic for almost everyone.
The learning curve for PS is very steep, there just is a lot less to focus on so the skills can be picked up fast, better maintained and seem to be less likely to degrade as much under stress.
With beginners, they often shoot faster and more accurate via PS because their minds are no longer in the way. Intermediate shooters is about the same, but at the intermediate level they would be at a disadvantage if they never practiced it before and were forced into it under stress. They haven't truly mastered their index yet. Advanced levels are where the most vehement opposition comes to PS because they honestly don't see the need for much, if any, PS practice based on their experience (and they are right). It's just that only a single digit percentage of the shooting population will get there and effective combat hit capability can be built with a lot less time and effort. Namely, add in some dedicated PS training and practice, then stress-innoculate it via FoF or other reality based simulation methodology.