Yes, if a course is taught according to WRSTC standards, then the divers should come out able to plan and execute dives at that level on their own, and it is up them to decide how they want to extend those limits, or even if they want to extend those limits. People often say that OW courses only teach beginning diver to follow DMs, but I don't remember the PADI OW course even mentioning following a DM as a possibility. Maybe it does somewhere, but I don't remember it.As I understand the WRSTC requirements, open water courses are supposed to create autonomous divers, one who can plan a dive in similar conditions to which they were trained. They are to be competent in planning dives, buoyancy (depth control), basic navigation, deploying a DSBM while neutrally buoyant without a significant depth change (couple feet at most), and can handle the basic emergencies for which they were taught to handle.
If they so wished, they could remain within the constraints of their open water certification and enjoy a lifetime of diving. At that level, there are enough dive sites throughout the world that even if they are teenagers, they will never run out of dive sites.
What happens after that initial training is what really matters. Some people go out immediately and practice independent (with buddy) diving. As for me, in my first couple years of diving, I only dived on vacations in Cozumel, where all dives are by law led by DMs, and those DMs do everything for you. After a couple of years, I did my first non-Cozumel dives in Florida, and I was pretty much out to the dive site before it became clear to me that no one was going to set my gear up for me. I then had to remember how the gear setup worked.
On a few occasions teaching dive planning in OW classes, I have had students tell me that their experienced diver friends assured them that they only had to do that stuff in class. After that, they could forget it all, because "in the real world," DMs do all that stuff. For many people, that is true. I am quite sure that there are divers with hundreds of dives over many years who have not set up their gear since OW class and who haven't the foggiest idea how to do any of the dive planning they were taught in their classes. It is not that their training was lacking--they had just learned over the years to be dependent upon others.