I have a number of thoughts about this topic.
1)Back in the "old days" an instructor was not supposed to take the beginner student to the open water unless they had perfected their skills in the pool. Then came the modular program where some learning occurred in the pool, but was supposed to be perfected at the open water. I have dealt with a lot of students at open water sites who had very poor skills (especially buoyancy). Thankfully, I could usually correct some of this and encourage them to take some specialty training to further perfect their skills.
For the record, some agencies are tying to change some of this. The SDI guidelines for instructors is that they are not sign a student off for open water unless they show complete mastery of skills in the pool. I am pretty comfortable that the Instructors I have trained will stick to this guideline. Not so sure I can vouch for other instructors.
2)I have run into a few divers in my teaching and trip escorting experiences whose cards should have been pulled, but alias that is not permitted (I once tried to do this).
3)I think the current trend of dive resorts and dive centers to recommend refresher classes if the diver has been inactive for 2 years or more is a good step.
4)As has been previously stated in other forums - we can't teach everything in the entry level class. Too much information overload would occur. But we should at least be sure they get the basics.
5) Bottom line is that we have to strive for instructors who are compitent and experienced enough to train their students properly.