I don't believe I'm creating a strawman. With regards to your question that I bolded, that in the majority of cases (over 50%), the answer is yes. The problem is that it is not an overwhelming majority.Again- you are bootstrapping the argument and creating a strawman. The issue isn't whether there are bad instructors and students who took their courses. The question is whether someone who is a certified diver can be presumed to know baseline diving as a general rule.
What you do as a boat operator is your business.If I am a boat operator, do you want me to pool test divers with a certification BEFORE letting them on the boat - even though they have a certification? Really?
What I will do when I open a dive center is take first time customers on an easy dive, unless they do a free workshop from shore to work out their weighting and I can observe their skills in the shallows. Mind you, this will be for an active retirement, so my goal is to simply not lose money. But that will be the way I operate, as while diving in the Med, there is often divers who cannot set up their gear and cannot control their buoyance, and that is a headache for the dive guide.