If I were to create a training and experience trajectory to guide a diver to achieve his or her own version of what a Master Scuba Diver might be, solely at the recreational level, it would be the following:
Certification Courses:
1. Watermanship: The gold standard would be passing a surf lifeguard course with a USLA-certified beach patrol, earning an EMT license, and working part-time or full-time for a couple of seasons as a surf lifeguard so rescues and assists become just another day at the office. The time and fitness standards might only be possible for younger divers who don't have family responsibilities. A silver medal would go to taking the American Red Cross Lifeguard Training course with the Waterfront add-on. Most rescues will find their way to the surface so having the swimming skills to make rescues is a must to be considered a Master Scuba Diver. An engineer friend of mine who was a PADI course director took my advice and went through a lifeguard class at the age of 50. He said I was right about the value. It changed the way he viewed safety in diving.
2. The next course would be a freediving course. Quality snorkeling and breath-hold diving education would create more confidence and teach the diver how to breathe better, relax, slow down, and become efficient in the water. The diver would also have the ability to dive deep without SCUBA to perform quick tasks such as recovering objects dropped over the side of a boat or make quick rescues without needing to gear up. Buy freediving gear! It will open up a whole unique world.
3. The third course would be a traditional open water course such NAUI, SSI, or PADI. This would put the diver on the same page as most entry-level divers in the world. Their materials are also easy to understand and learning is not that difficult. Don't buy gear. Just a mask with a better field of vision than a freediving mask and Jet style fins.
4. Time for nitrox! The best nitrox course will kill two birds with one stone. Take a GUE-F course and dial in your trim, buoyancy, and propulsion skills. Buy your gear and start breathing a better gas.
5. Now, you can pursue advanced open water. The most important part of advanced diving is navigation. You can practice in the woods with your dive compass before class. If you get good at the compass courses Eagle Scouts often install in state parks as projects, you'll be on your way. Learn to swim straight lines and to navigate while swimming at 15 feet (safety stop depth) while keeping your team together. Squares and triangles are built on straight lines. The goal is to be able to locate a vertical line rather than a large object. Quarries are excellent for this. Choose an AOW instructor who has a cave or DIR background so you'll learn to use lights at night like a cave diver. You'll need search & recovery to be a Master Scuba Diver. A public safety diving instructor is often very good at rigging heavy anchors and such because they can raise cars. Equipment repair and maintenance are also a must. You need to be able to fix your wetsuit or drysuit. Stay wet for now. Don't combine AOW with drysuit. Bad things can happen. Add another elective that interests you.
6. Do 5 specialties. If you live where it is cold you might want a drysuit at this point. SDI Solo with a TDI cave instructor might be fun, cavern, wreck diving, ice diving, drift diving, or anything that directly applies to your interests or where you will be diving most.
7. Last class: Rescue diver! Find the toughest instructor you can find who will make it as physically demanding as possible.
Experience:
There are two types of expert divers. The first is the diver who makes his or her home waters more or less the whole world. They may not have the ability, desire, or means to travel but they know every coral head, kelp frond, or blue gill in their backyard.
The second type of expert is the one who racks up dives in lakes, rivers, quarries, and the ocean in both temperate and tropical waters around the world. They can pretty much go anywhere and they feel at home and at ease everywhere they go. They may know everyone on 5 continents.
Once you find yourself in such a diving routine that it might even feel like a rut, but you don't know what else to do with yourself, and everyone (even the instructors) are the ones asking you questions about how deep the wreck is at the prop, how do you fix a nylon float, and where you are going to eat, you are almost a Master Scuba Diver.
When you look around after all of that and realize you are the one having the most fun, you nailed it! Give yourself a card. Make it fancy.