In that thread I made a
Post detailing the core skills someone should have gained proficiency in. They don't need to be "demonstration standard" but should be achievable even when lightly task loaded
And yes there is a degree of mindset - being somewhat conservative and adhering to the lessons learnt within your basic training.
Some people will never be proficient or advanced because they don't have the interest. Let me explain:
I used to play golf. I had numerous lessons my own gear and went out and played regularly. But I was never more than a hack and basher, because I didn't care enough about it all. To me golf was a walk outside with friends, hitting a ball as a means to work up an appetite for the 19th hole. A lot of divers are like that too.
People cite Fundies as a remarkable course. Without being disingenuous to the training nor those who participate, in effect its a basic course (taught well). However if you have invested $2000 in the course and travel accom etc, plus 5 vacation days, you are pretty incentivised to learn, and you have a desire to.
Normal training is fairly cheap and so the incentive isn't always there. Furthermore you can teach someone (if they want to learn) but you can't make them continue to practice afterwards - thus skills become rusty.
The mindset and desire to constantly improve oneself and become a better diver is what separates the few from the many.