This is a very thought-provoking thread, and the question asked is very reasonable. The thread produces six, somewhat visceral, reactions:
1. Hindsight is always (at least) 20/20, often it is 20/15. If I had known then what I know now, I might have done some things differently. Oh, dang, I forgot, we are talking about diving, not life in general.
2. I 'WISH' I had been born rich. Then I wouldn't have to allocate my financial resources in a somewhat thoughtful manner. I would just buy anything I wanted, and take any class I wanted, and travel anywhere I wanted, etc., etc., etc.
I wish my PADI open water instructor had knowledge of this type of diving, I might have learned appropriately.
3. At the risk of sounding like a PADI apologist, I would expand the wording of this question to include virtually all agencies and instructors. I don't know if your 'PADI Instructor' had knowledge of this type of diving, or simply (and not unreasonably) worked to prepare you to be a reasonably competent, reasonably safe OW diver - according to the general practices and standards of the certifying agency - who could then go forward and learn more, including more about different types of diving, different types of gear, etc. I think the statement applies to most agency training, not just PADI.
4. I 'WISH' - because I now believe it to be an absolute truth
)) - that ALL OW students were trained using a BP/wing, and a regulator configuration with a long(er) hose used as a primary and a bungeed necklace used generically as an alternate. For OW, recreational diving, I now believe that integrated alternate air sources / inflators are the devil's work, that the I3 is a major hindrance to the ability of any diver to advance from a novice to a competent manager of buoyancy and trim. (Please, those of you who use those, TAKE NO OFFENCE; I am engaging in a bit of hyperbole for the sake of discussion.)
What challenges or frustrations led you to "wish" something had happened differently along the way in your diving career thus far?
5. Realistically, I 'WISH' I has started diving earlier. That is another matter, entirely, however.
6. I 'WISH' I had more time and money to formally train - take courses that are - NOW - of interest to me. Those courses would not have been of any interest to me as an OW student, however. But, like several others, I appreciate the intrinsic learning value that has come through my meandering development as a diver. I believe I am a better diver as a result and - more importantly - I am a better instructor as a result.
What would I want to have 'happened differently' along the way in my diving career (and what I now try to do as an instructor because I have the benefit not only of the experience of how I trained, but also the experience of what I have subsequently learned - which wouldn't have meant anywhere near as much had it not been for how I was originally trained):
a. More emphasis on buoyancy control AND TRIM at the OW level.
b. Earlier introduction to the variety of gear configurations available.
c. Greater emphasis on efficient propulsion techniques at the AOW level.
d. More opportunities for informal 'workshop' learning at the OW level.
I spent a significant portion of my adult life as a tenured member of the faculty of a nationally prominent health science school in a major state university. I often heard faculty colleagues (usually, the younger 'climbers') tell students that they prepared for their career from 'Day 1', and that hard work, and a clear sense of direction were critical to success. I, on the other hand, have always told my students that my (more than moderately successful, if I may be so immoderate) career was a lucky accident. The key was being prepared to adapt to whatever came my way. I am humbled by many things, but seldom embarrassed by what I do not (yet) know. There are people who write entire books about things that I do not (yet) know. I am ALWAYS frustrated by what I have yet to learn - so much to learn, so little time. Maybe, I should be a Buddhist.