Since you quoted me, I try to clarify a bit my position. The topic here is "how to become a better diver", and I (we?) am (are?) trying to assess pros and cons of the DM course vs basic technical training in terms of:
- theoretical knowledge
- diving skills
- awareness
I don't see any problem here. But I didn't get any answer yet...
What is a bad buoyancy control for me in his context? Well, when a diver
needs to kneel to perform tasks. Why do I think this is bad? Because I assume that, if one has good buoyancy control, wouldn't even think about kneeling - stay neutral would be automatic. Is my definition of "bad"
the absolute definition? Absolutely no.
I met divemasters with buoyancy control worse than mine, and (very) few of them were bad according to my definition. Now, I am not a divemaster - but I have basic technical training. So I need to think that, at least in principle, the DM course is not necessarily better than basic tech/cave training in terms of skills, especially buoyancy. I am trying to figure out if this is the norm or not, that's it.
If you have never met DM with poor skills, well... maybe I was unlucky? I don't know, it's just my experience and I am sharing it
I did my Tec 40 before DM so the following is from that specific point of view:
Theoretical Knowledge:
There is a large study component and related examination in DM around diving general knowledge; e.g. what causes tides, ecosystems, dive physiology and physics, decompression theory, gear, dive planning with tables and RDP. I think it's good to have all that breadth and depth as a diving professional.
Tech knowledge development focuses on gear, thinking like a tech diver, redundancy, planning, decompression theory, and of course on techniques for planning and executing decompression dives.
Diving Skills:
There aren't any specific dive skill performance requirements for completing DM. You are formally evaluated on things like comfort in water (various swim tests) and ability to demonstrate 24 skills that are part of the OW course, then there are practical evaluations like being able to lead dives. There is no expectation of doing skills neutrally buoyant (though there may be bonus points for doing so), and there is no part of DM that focuses on diving skills improvement unless you're particularly deficient in something that the instructor notices and feels is important to work on.
DM is focused on leadership and judgement first and foremost, which contribute to your main job, supervising and conducting safe dives and dealing with related problems. A secondary component would be assisting instructors mostly in class management and teaching the handful of skills you're permitted to teach. A major non-skills component of DM education is the professional side: learning about the agency's standards and rules, what you can and cannot teach, instructor-to-student ratios, course prerequisites, sales, customer service.
Will your in-water skills improve in DM? Most likely, but more as an indirect result of pool/OW time, extra task loading, situational awareness, and needing to be a good example to others at all times. The responsibility is on you to know what you have to improve. So there's no surprise that you find anyone, DM or otherwise, possibly lacking because they might not have had a good model or instructor. I certainly needed someone to point out issues with my technique that I couldn't notice without their help or video proof. Also, don't forget dive shop training or regional variations - up here in the PNW, divers are preconditioned to be neutral or use 2 fingers to avoid stirring up the bottom, so the DM's will hopefully continue to model that through their own training.
Tech, on the other hand, will expand your diving skills envelope, no question, due to specific skills that are performance requirements for the course. You said you've got basic tech, so I won't go into the list, but the ability to have a controlled ascent with multiple stops, switch gases, deal with problems without surfacing, and work as a team while under time, gas, and buoyancy variation limits are valuable and personally rewarding skills to have (once you master them) but certainly not part of the basic DM's skill requirements.
There is overlap between Tech and DM around the dive planning and logistics of course, with the exception of the decompression planning. All good divers should at least have a plan in their heads, so neither differs much in the broad strokes: minimum gas reserves, dive briefings, appropriate site selection, dive goals, environmental considerations, emergency preparedness, etc.
Awareness:
As I already mentioned, DM stresses awareness of problems and anticipating problems. On a DSD or DLD dive your students/customers expect you to conduct a safe and fun dive. You need to be able to fix the gear, adjust their buoyancy before it's a problem, track their gas usage, not get lost, show them cool stuff, etc. The buck now stops with you, and that is a significant mindshift and chance to grow in that leadership space.
Tech stresses similar awareness, the different assumption is your team is fairly independent and skilled and not liable to be bouncing off coral or running out of gas, but you still need to be aware of your team members, be in passive contact with them (using your lights, for example) and your positioning relative to them to be able to instantly respond to problems. You may assign different responsibilities on the dive, like bottom captain and deco captain, but everybody is assumed to have a say in the conduct of the dive and speak up during and after the dive.
My Take:
If you want to acquire a broad skills repertoire, I agree with others that mention Rescue + basic technical cert like a PADI Tec 40. I strongly believe the knowledge, mindset and skillset you acquire in tech are important for being an environmentally considerate thinking diver that isn't reliant on others for executing a safe and fun dive, whether within rec limits or not.
If you feel your leadership skills need a boost, then DM is good for that particular aspect, but be aware it is targeted to the professional skills realm, and if you have no interest in agency standards, that part will be a waste of time. Of course, you'll still be an improved diver as a DM in that your overall skills, knowledge, confidence in handling many different situations, and awareness will be greater than when you started.
My particular road passed through GUE Fundamentals before PADI TecRec, and Fundamentals solidified a lot of the core diving skills list above prior to taking tech. So I do recommend Fundies or similar core or pre-tech courses offered by agencies or LDS (my LDS developed a great specialty akin to Fundies) and it isn't a bad place to pause, get more experience with the improved skills, before considering if you want to move into tech training.